On March 2, 1979, the district attorney for the Plymouth District (district attorney) obtained an order from a judge of the Superior Court, pursuant to a motion to compel technical assistance, directing the New England Telephone & Telegraph Company (company) to assist the district attorney in the installation of a cross frame unit trap or similar device on a particular telephone line. A cross frame unit trap records the telephone numbers of incoming calls, or attempted incoming calls, to a telephone line under surveillance. The company argues that the judge had no authority to enter the order. We conclude that the judge had that authority and, in the circumstances, acted within his discretion.
We summarize the background as set forth in the judge’s memorandum of decision and report.1 In early 1979, the district attorney was engaged in an extensive criminal investigation into illegal gaming operations in Plymouth County. On February 16, 1979, a judge of the Superior Court issued a warrant and order, pursuant to G. L. c. 272, § 99E, authorizing the interception of wire communications to and from the telephone number which was subject to the warrant. That order also explicitly authorized “the installation of a pen register or other device, if practicable, designated for the purpose of ascertaining the telephone *588numbers called by the subjects . . . and the telephone numbers of instruments used in making calls to the suspect telephone in furtherance of the conspiracy.” While the wiretap warrant was in the process of being executed, the district attorney sought and obtained the order compelling the company to provide technical assistance in installing a cross frame unit trap in the company’s Brockton switching station. This installation would result in the recording of the numbers of certain incoming local calls.2
1. Constitutional considerations. The company advances no constitutional arguments.3 It does not contend that the State lacks constitutional authority to require compensated assistance from it, but only that the judge had no statutory authority to do so. The Supreme Court of the United States has upheld a Federal court order directing a telephone company to provide Federal law enforcement officials assistance in implementing an order authorizing the use of a pen register. United States v. New York Tel. Co., 434 U.S. 159 (1977). Neither the opinion of the Court nor the dissenting opinions indicate that, assuming appropriate authority for a court to enter such an order, there is any significant Federal constitutional problem. The principal dissenting opinion refers to art. 14 of the Massachusetts Declaration of Rights, concerning unreasonable searches, and suggests, in light of historical abhorrence to “general warrants” and “writs of assistance,” that courts should be reluctant to imply authority for court orders commanding *589third-party assistance to law enforcement officials. United States v. New York Tel. Co., supra at 180 and at 190 (Mr. Justice Stevens dissenting in part).
The company does not, and arguably cannot, present constitutional objections which might be advanced by others, most particularly the argument that the recording of the source of an incoming call is an unreasonable search in violation of the constitutional rights of a person who dials the subject telephone number. It must be granted that, in many instances, the caller will never learn of the intrusion and that, unless considered in a preinstallation proceeding such as this, his or her constitutional rights might be infringed without any opportunity for judicial protection. The Supreme Court of the United States has recently held, however, that the use of a pen register in a telephone company office (to record numbers dialed from a particular line) is not a search within the meaning of the Fourth Amendment. Smith v. Maryland, 442 U.S. 735 (1979). We earlier had suggested, in a contrary tone, that the use of a pen register required compliance with the probable cause requirements of the Fourth Amendment (see Commonwealth v. Vitello, 367 Mass. 224, 279 n.33 [1975]). Presumably, the Supreme Court would not regard the installation of a cross frame unit trap at a telephone company office as a search in the constitutional sense. See Smith v. Maryland, supra at 741-746.
We, of course, might adopt a broader definition of search under art. 14 of the Declaration of Rights than prevails under the Constitution of the United States. See Commonwealth v. Ortiz, 376 Mass. 349, 358 (1978). The amicus brief filed by the Civil Liberties Union of Massachusetts urges us to do so and to strike down the order on State constitutional grounds.
The record in this case, however, provides no adequate basis for reaching any conclusion about the constitutional rights of persons who dial the number of the surveyed telephone line. We do not have before us the information on which probable cause to survey the telephone line was *590based. We know that a judge of the Superior Court thought it sufficient to conclude that a wiretap was justified in the circumstances, and he issued an order and warrant to that effect. Thus, actual conversations on the telephone line were monitored and perhaps recorded. This process included incoming, as well as outgoing, calls. The monitoring and recording of such calls constitute, at least in most instances, a greater intrusion into a caller’s privacy than does the use of a cross frame unit trap (United States v. New York Tel. Co., 434 U.S. 159, 170 [1977]), and the installation of a wiretap according to statutory procedures has withstood constitutional challenge. See Commonwealth v. Vitello, 367 Mass. 224, 244 n.5 (1975). Compliance with statutory requirements itself affords considerable protection against any unconstitutional intrusion. Consequently, we decline in this case, where statutory procedures were followed in obtaining the right to survey the subject telephone line, to pass on the possible rights of third persons to object on State constitutional grounds.4
2. Statutory authority. The company contends that a judge of the Superior Court lacks authority to issue an order *591directing it to assist in the installation of a cross frame unit trap. Some of the company’s arguments seek our reconsideration of conclusions reached in New England Tel. & Tel. Co. v. District Attorney for the Norfolk Dist., 374 Mass. 569, 573-574 (1978). There, we held that a judge of the Superior Court had authority to order the company to provide technical assistance to law enforcement officers to make an unobtrusive wiretap pursuant to a warrant issued under G. L. c. 272, § 99. We followed in substance the reasoning of the Supreme Court of the United States in United States v. New York Tel. Co., 434 U.S. 159 (1977). We adhere to our earlier decision and discuss only those arguments which seek to distinguish the case before us from that earlier one.
The company argues that an order concerning the installation of a cross frame unit trap is not authorized by G. L. c. 272, § 99, and asserts that § 99 occupies the field of statutory authority in Massachusetts. The wiretap order in New England Tel. & Tel. Co. v. District Attorney for the Norfolk Dist. was clearly authorized by § 99. We have already held that a separate order under § 99 authorizing the use of a pen register by law enforcement officials is not required where a valid order authorizing a simultaneous wiretap interception has been issued pursuant to applicable Federal and State statutes. Commonwealth v. Vitello, 367 Mass. 224, 279 (1975). There is no compelling reason to treat a cross frame unit trap any differently in this respect from a pen register.
We agree with the judge below that § 99 expressly authorizes a court order concerning the installation of a cross frame unit trap. The exceptions to the prohibitions of § 99 include “any person duly authorized to make specified interceptions by a warrant issued pursuant to this section.” G. L. c. 272, § 99 D 1 d, as appearing in St. 1968, c. 738, § 1. An interception is defined, with certain irrelevant exceptions, to include the secret recording of “the contents of any wire or oral communication through the use of any intercepting device” (emphasis supplied). G. L. c. 272, § 99 B 4. “Con*592tents” in turn is defined broadly to include, among other things, “any information concerning the identity of the parties to such communication or the existence ... of that communication.” G. L. c. 272, § 99 B 5. It is true that the information recorded by a cross frame unit trap (or a pen register) does not always establish that there was an oral communication, because the dialed call may not have been completed. However, the recording of the telephone number of the line from which a call was attempted is “information concerning the identity of” a party to a communication and concerning “the existence ... of that communication.” Even if the call is not completed, the caller has initiated a wire communication to the surveyed telephone line which is intended to cause that telephone to ring and the existence of that communication is recorded by an intercepting device.
Our conclusion that a cross frame unit trap is regulated by the Massachusetts wiretap statute is based on differences between our statute and the Federal wiretap statute. The Federal wiretap statute defines “intercept” as relating only to the “aural acquisition of the contents of any wire or oral communication” (emphasis supplied) (18 U.S.C. 2510[4] [1976]) and is thus inapplicable to pen registers and to cross frame unit traps. See United States v. New York Tel. Co., 434 U.S. 159, 166 (1977) (pen register); Michigan Bell Tel. Co. v. United States, 565 F.2d 385, 388 (6th Cir. 1977) (trapping or tracing incoming calls).5 Our statute, as quoted above, contains no such limited definition of “ inter*593ception.” We view the distinction as meaningful and are strengthened in our decision to treat cross frame unit traps as governed by § 99 because to do so will ensure that the procedural protections of § 99 will be available to the users of telephones in this Commonwealth and that the company will be subject to judicial orders only in cases where the conditions of § 99 have been satisfied.6
The basic issue here is not so much the question whether a judge of the Superior Court may by order permit the installation of a cross frame unit trap as it is whether, under the statutory law of the Commonwealth, the company may be directed to assist in that effort, assuming proper compensation for its services. Our decision in New England Tel. & Tel. Co. v. District Attorney for the Norfolk Dist., 374 Mass. 569 (1978), and our previous discussion of § 99 as applied to this case direct an affirmative answer to that question.7
Although a judge of the Superior Court may require the company to assist in the implementation of an order entered pursuant to § 99 by installing a cross frame unit trap, the *594decision whether to enter such an order lies in the judge’s sound discretion. The judge should consider the nature of the crime, whether the attempt is likely to be worthwhile (which may depend on the sophistication of the available equipment), the burden on the company, the cost to the Commonwealth, and the threat to the privacy of innocent third parties. In considering the threat to the interests of innocent third parties, the judge should consider whether the Commonwealth has demonstrated a substantial likelihood that it needs to obtain the numbers of one or more telephones from which incoming calls are made. The company argues that it does not want to act as an agent for prosecutors and that its personnel may become subject to improper pressures from criminal elements to disclose surveillance activities which, when a cross frame unit trap is involved, cannot readily be concealed within the company. These considerations are relevant and might be persuasive in obtaining legislative protection for the company. But it is also true that the company has a special monopoly status, and, in many instances, it alone has the equipment and skills necessary to carry out an operation which a judge has determined is reasonably required. In this case, particularly where the task was not onerous, the determination to order the company to assist law enforcement officials was within the judge’s discretion.
3. Conclusion. The order of the Superior Court judge directing the company to provide such technical assistance as may be necessary for the installation of a cross frame unit trap or similar device is affirmed.
So ordered.
The judge reported the case to the Appeals Court for a determination of the propriety of the order. We granted the company’s request for direct review. Although the period of the effectiveness of the order has expired, and the company has complied with the order, and, therefore, the case is technically moot, it is appropriate to pass on the question before us because, in the normal course, any such order will be incapable of timely review and yet the issue is likely of repetition. See Superintendent of Worcester State Hosp. v. Hagberg, 374 Mass. 271, 274 (1978); United States v. New York Tel. Co., 434 U.S. 159, 165 n.6 (1977).
The equipment at the Brockton switching station was more sophisticated than that at certain other company switching stations, and the tracing process, therefore, was far easier than it would have been in many other situations. Only about one half the inhabitants of greater Brockton were served by the Brockton switching station in which the cross frame unit trap was to be located. Only the numbers of incoming calls dialed within the switching station’s service area would be recorded.
The company opposed the district attorney’s request for assistance, and it makes no claim that it was not afforded an adequate hearing on the issue of the burdensomeness of the order before the order was entered. See In re Application of the U. S. for an Order Authorizing the Installation of a Pen Register or Touch-Tone Decoder & a Terminating Trap, 610 F.2d 1148, 1157 (3d Cir. 1979).
The issues presented by the parties do not concern the lawfulness of the original wiretap order. The dissenting opinion argues that this court should decline to answer the questions presented until it is clear that that wiretap order was lawful. The case is technically moot. A remand for further findings of fact would be a waste of judicial resources.
We reject the dissent’s suggestion that the court’s opinion will encourage dragnet surveillance of telephone subscribers without probable cause. In view of the statutory requirements for telephone surveillances, we perceive neither the threat of a dragnet nor the want of findings of probable cause which the dissent imagines. These statutory requirements are not inconsiderable. The dissent implies that these statutory requirements may not comport with the requirements of the State Constitution, raising doubt about the constitutionality of all wiretaps. This case simply does not present this issue. The case involves only the question of the State’s right to direct the tracing of telephone numbers of incoming calls which were already being monitored pursuant to an unchallenged court' order. Thus, apart from the order against the company, every word spoken in every conversation involving the surveyed telephone was subject to being heard, and recorded, by investigating authorities. The identity of the callers might be ascertained and information far more personal than a telephone number might be noted.
The New Jersey Wiretapping and Electronic Surveillance Control Act, N.J. Stat. Ann. § 2A:156A-1 et seq. (West 1971), similarly defines “intercept” as involving the “aural acquisition” of the contents of any wire or oral communication. In light of that restriction, in In re In-Progress Trace of a Wire Communication, 76 N.J. 255 (1978), the majority opinion held that no court in New Jersey had authority to require a telephone company to conduct an in-progress trace of a call coming into a telephone which was being subjected to a court authorized wiretap. An amendment to the New Jersey statute, enacted shortly after that decision, places an obligation on a telephone company in certain circumstances to provide an in-progress trace during an interception. N.J.P.L. (1978) c. 51, § 5, amending N.J. Stat. Ann. § 2A:156A-12 (West 1971).
We have noted that a State wiretap statute properly may adopt standards that are more restrictive than the requirements of Federal law (Commonwealth v. Vitello, 367 Mass. 224, 247 [1975]) and that in certain respects our statute imposes more stringent restrictions on the use of electronic surveillance devices than exist in certain other jurisdictions (Commonwealth v. Jackson, 370 Mass. 502, 506 [1976]).
Under the Federal law, courts have found authority in Fed. R. Grim. P. 41 and in the All Writs Act, 28 U.S.C. § 1651(a) (1976), or in analogous “inherent powers” of the Federal courts, to support an order directing a telephone company to assist in the installation of electronic surveillance devices not covered by Title III of the Omnibus Crime Control and Safe Streets Act of 1968, 18 U.S.C. §§ 2510-2520 (1976). See United States v. New York Tel. Co., 434 U.S. 159, 171-178 (1977) (pen register); Michigan Bell Tel. Co. v. United States, 565 F.2d 385, 389 (6th Cir. 1977) (tracing device); Application of U.S. v. Southwestern Bell Tel. Co., 546 F.2d 243, 246-247 (8th Cir. 1976) (pen register); United States v. Illinois Bell Tel. Co., 531 F.2d 809, 814 (7th Cir. 1976) (pen register); Application of U.S., 458 F. Supp. 1174, 1176 (W.D. Pa. 1978) (tracing device). We need not consider whether the order in this case could be supported by parallel reasoning under G. L. c. 276, § 1, and G. L. c. 220, § 2, because we conclude that § 99 supports the entry of an order concerning the cross frame unit trap in this case.