delivered the Opinion of the Court.
The People bring this interlocutory appeal pursuant to C.A.R. 4.1 to challenge a suppression ruling made in the course of a pending criminal case -in which the defendant, Thomas Titus (Titus), was charged with possession of marijuana with intent to distribute or sell1 and possession of marijuana.2 The trial court ruled that the affidavit underlying the warrant to search Titus’ residence did not establish probable cause, and suppressed the evidence seized during the search. The District Attorney for the Fourth Judicial District, El Paso and Teller Counties, then filed this interlocutory appeal. We affirm the ruling of the trial court suppressing the evidence and hold that the warrant to search Titus’ house was not supported by probable cause.
I.
In July 1993, the Colorado Springs Police Department received a letter from a first-time anonymous informant alleging that the occupants of 716 Arcadia Place, Colorado Springs, were engaged in selling marijuana. The informant stated that she had observed a large number of visitors to the home, who stayed for short periods of time. The informant included in the letter a list of the license plate numbers of approximately twenty cars belonging to the visitors, and descriptions of the vehicles. Additionally, she stated that on several occasions she had smelled the odor of burning marijuana coming from the residence.
Detective Curtis Richter cheeked the license plate numbers provided by the informant in a computer data base and found that they matched the descriptions of the vehicles given by the informant. The anonymous informant later provided two more lists of vehicle license plates and descriptions, which Detective Richter also confirmed. He determined that approximately forty-seven different vehicles had stopped at the residence in the one-month period between late July 1993 and late August 1993.
On the afternoon of August 22, 1993, Detective Richter sent a police informant to 716 Arcadia Place to try to buy marijuana from the defendant, who happened to be holding a yard sale that day. The police informant was wearing a hidden tape recording device. According to Detective Richter’s affidavit to support the warrant, the following conversation took place between the police informant and Titus:3
Cl [Confidential Informant] asked the male if the property out in front was for sale, specifically a VCR. The male party stated that the VCR was for sale, and Cl asked, “Are you Tom?”. The male replied, “Yeah”, and Cl told Tom Titus that he was a friend of “Barb’s”, which was the first name of a person whose license plate had been seen at Titus’ residence by Crime Stopper # 1789E. At that time, Tom Titus stated, “Oh, uh, Mimi”.
At that time, Cl stated, “I’ll buy that (the VCR), and can you get me a quarter?”, meaning a quarter ounce of marijuana. Titus stated, “No.... don’t have any”. Cl, at that time, asked, “Can I get some later, if I bring Mimi?”. Tom Titus stated, “We’ll see, if you bring Mimi”. CI[ ] and Tom Titus then continued to talk about the VCR, and several seconds later, Cl asked again for a quarter ounce of marijuana. Tom Titus told Cl, “That’s something I won’t do ... I’ve got hard and pat rules about that”.
At that time, Cl stated, “I’ll give you sixty for both, just an eighth (meaning an eighth of an ounce of marijuana[) ]”. Cl stated further, “I want to get high, man”. Tom Titus then stated to Cl, “I can’t do it ... bring Mimi”.
Cl continued to talk to Tom Titus about the marijuana, and Titus told Cl, “To this date in my life, I’ve dealt with a very select *150group of people ... I don’t need new customers ... so, bring Mimi”.
The affidavit also stated that Detective Richter conducted surveillance of the house between August 1 and August 30, stopping three times and remaining between one-half and one hour each time, but saw no activity. On October 11,1993, Detective Richter spoke again with the anonymous informant, who reported that the number of visitors to 716 Arcadia Place continued unchanged.
The affidavit also reported that Titus is self-employed and operates a telephone repair business out of his home.
Additionally, Titus’ attorney stated at the suppression hearing that the anonymous informant has had a “long-standing feud” with Titus.
Detective Richter applied for a warrant to search the residence on October 15, 1993, and a county judge signed the warrant. On October 21, 1993, officers of the Colorado Springs Police Department executed the warrant. They seized approximately two ounces of marijuana (58.1 grams), a triple beam balance, and a box of Ziploc baggies. Titus told police that the marijuana belonged to him and that he purchased approximately four ounces of marijuana each month for personal use.
Titus was charged with possession of marijuana with intent to distribute or sell, and possession of marijuana. The trial judge granted Titus’ motion to suppress the evidence on the grounds that sufficient probable cause did not exist to support issuance of the search warrant.
II.
The issue before us is whether the affidavit submitted by Detective Richter contained sufficient information to support a finding of probable cause to issue the search warrant. We do not review the decision of the county judge de novo; rather, it is the task of a reviewing court to determine whether the judge who issued the warrant had a substantial basis for concluding that probable cause existed. People v. Abeyta, 795 P.2d 1324, 1327 (Colo.1990).
The determination of probable cause must be made from the four corners of the affidavit. People v. Lindkolm, 197 Colo. 270, 273, 591 P.2d 1032, 1034 (1979); People v. Brethauer, 174 Colo. 29, 39, 482 P.2d 369, 373-74 (1971). Probable cause exists when an affidavit alleges sufficient facts to warrant a person of reasonable caution to believe that evidence of criminal activity is located at the place to be searched. Abeyta, 795 P.2d at 1327; People v. Quintana, 785 P.2d 934, 937 (Colo.1990). When the information in an affidavit is based on the reports of an informant, a judge considers the “totality of the circumstances” and asks the common-sense practical question of whether, through the eyes of a reasonable police officer, there is probable cause to issue a warrant. Illinois v. Gates, 462 U.S. 213, 103 S.Ct. 2317, 76 L.Ed.2d 527 (1983) (abandoning formal application of the two-pronged test enunciated in Aguilar v. Texas, 378 U.S. 108, 84 S.Ct. 1509, 12 L.Ed.2d 723 (1964), and Spinelli v. United States, 393 U.S. 410, 89 S.Ct. 584, 21 L.Ed.2d 637 (1969)). We adopted the Gates totality-of-the-cireumstanees test in People v. Pannebaker, 714 P.2d 904 (Colo.1986).
Even if an informant’s allegations do not establish probable cause by themselves, it may be possible to obtain a warrant by corroborating the details of the tip through independent police work. Gates, 462 U.S. at 241-42, 103 S.Ct. at 2333-34. Police corroboration of significant aspects of an informant’s tip is an important factor in the probable-cause calculation, but it is not a constitutionally required, indispensable component. People v. Paquin, 811 P.2d 394, 398 (Colo.1991). Neither is it necessary that police corroborate evidence relating directly to illegal — as opposed to innocent — conduct alleged by the informant. People v. Turcotte-Schaeffer, 843 P.2d 658, 660-61 (Colo.1993). Under the totality-of-the-circumstances test, it is possible to establish probable cause solely through corroboration of non-criminal activity. Id.
III.
Based on the four corners of the affidavit and the totality of the circumstances, we agree with the trial judge that the infor*151mation contained in the affidavit was not sufficient to establish that probable cause existed to support the issuance of a search warrant for Titus’ residence.
A.
We begin by recognizing that the police had no indication, apart from the anonymous informant’s suspicions and the police informant’s conversation with Titus, that Titus was engaged in criminal activity. Unlike Pannebaker or Turcotte-Schaeffer, for example, the anonymous informant in this case did not claim that Titus had ever sold marijuana to her, nor that she had ever seen Titus selling marijuana to anyone. Furthermore, the attempt by the police to manufacture a sale by Titus was unsuccessful. No sale ever took place, and Titus made no agreement to sell marijuana to the police informant posing as a buyer.
Cl stated, “I’ll buy that (the VCR), and can you get me a quarter?”, meaning a quarter ounce of marijuana. Titus stated, “No_don’t have any”. Cl, at that time, asked, “Can I get some later, if I bring Mimi?”. Tom Titus stated, “We’ll see, if you bring Mimi”. CI[] and Tom Titus then continued to talk about the VCR, and several seconds later, Cl asked again for a quarter ounce of marijuana. Tom Titus told Cl, “That’s something I won’t do ... I’ve got hard and pat rules about that”.
At that time, Cl stated, “I’ll give you sixty for both, just an eighth (meaning an eighth of an ounce of marijuana[) ]”. Cl stated further, “I want to get high, man”. Tom Titus then stated to Cl, “I can’t do it ... bring Mimi”.
Cl continued to talk to Tom Titus about the marijuana, and Titus told Cl, “To this date in my life, I’ve dealt with a very select group of people ... I don’t need new customers ... so, bring Mimi”.
Although Titus’ remarks create an inference that Titus was engaged in criminal activity, absent anything further than reasonable suspicion, the conversation does not— either by itself or when considered with the other evidence — establish probable cause to support the issuance of a search warrant for Titus’ residence. See United States v. Barker, 623 F.Supp. 823, 843 (D.Colo.1985) (concluding that, although telephone conversations between defendants, as described in an affidavit, clearly supported a finding of probable cause to believe the defendants were involved in drug transactions, the affidavit did not provide probable cause to search a residence when the conversation contained nothing to indicate that contraband or drug-related items would be found at the residence).
B.
We next consider the high volume of traffic reported by the anonymous informant, and whether it supports a finding of probable cause. According to information supplied by the anonymous informant, people from forty-seven different vehicles visited Titus’ house in a one-month period. Several of them had been observed at the house more than once.
The fact that a large number of people visit a residence in a one-month period does not establish that illegal activity is taking place. This type of information in affidavits originated during the prohibition era. Today, there must be something more than the mere fact that people are coming and going in order to support the belief that criminal activity is occurring. See People v. Broilo, 58 Mich.App. 547, 228 N.W.2d 456 (1975). Such additional evidence may include the observance by police or informants of criminal or other suspicious activity. In a case such as this one, in which Titus reportedly operated a business out of his home, large numbers of visitors would not suggest illegal activity.
Detective Richter stated in his affidavit that he was able to verify that the license plate numbers of the vehicles on the list of the anonymous informant matched the descriptions of the vehicles that she gave him. There is nothing in the affidavit to suggest, however, that any of these vehicles belonged to known drug offenders, or were used in the furtherance of any illegal activity. Although it is not clear from the record, either Detective Richter did not search his computer data base to determine whether the vehicle owners had prior convictions for marijuana of*152fenses, or he did search for this information, and found that Titus’ visitors had no prior drug offenses. In the end, Detective Richter’s investigation merely confirmed that the vehicles had the correct license plates attached, and no more.
Detective Richter also did not corroborate the informant’s assertion that any of the vehicles on the informant’s list had ever visited Titus’ residence. In fact, during Detective Richter’s surveillance of the house, he never saw any visitors at Titus’ residence. Even if the informant had merely copied down license plate numbers and vehicle descriptions from autos in a grocery store parking lot, the detective’s cursory “investigation” would not have discovered this deceit.
The matching of vehicle license plate numbers with vehicle descriptions was not the kind of “police corroboration” that would serve to establish probable cause in this case. Absent any additional corroboration — for example, that the owners of the vehicles were involved in illegal activity — it was insufficient to support a finding of probable cause.
C.
The only possible evidence of criminal activity referred to in the affidavit is the anonymous informant’s statement that she had “on several occasions ... smelled the odor of burned marijuana coming from the residence.” The affidavit does not state the circumstances under which the informant smelled the odor of burned marijuana. Nor does it disclose how many times she smelled it. Most importantly, however, it does not disclose when these olfactory experiences took place. There is no indication that the police officer attempted to determine whether the informant had smelled marijuana burning recently, or whether the event was remote in time.4
The affidavit reported that the anonymous informant had told the officer that she was “familiar with the smell of burning marijuana, as [she] had been exposed to marijuana in
the past, through acquaintances.” As Titus points out in his brief, however, there is no evidence that the informant is knowledgeable about the identification of smells. He asserts that, even if there was a smell coming from the house, it could have originated from another substance.
Without more, such vague claims of the informant’s smelling of burning marijuana “on several occasions” add little to the probable-cause equation. Under no circumstances do they support the conclusion that Titus was selling marijuana out of his home. Had the informant seen marijuana being used or participated in a sale, the analysis of whether there was probable cause may have been different. However, those conditions are not present here.
IV.
The People contend that, even if there was not probable cause to support the issuance of the warrant, the evidence should not be suppressed because of the good-faith exception to the exclusionary rule. The good-faith exception, enunciated in United States v. Leon, 468 U.S. 897, 104 S.Ct. 3405, 82 L.Ed.2d 677 (1984), and enacted into law by our legislature in section 16-3-308, 8A C.R.S. (1986), applies when police were acting in reasonable reliance on a search warrant issued by a detached and neutral magistrate or judge, and the warrant is later found to be unsupported by probable cause. The good-faith exception is applicable only when the officer’s reliance on the warrant is objectively reasonable. Leon, 468 U.S. at 922-23, 104 S.Ct. at 3420-21.
The issue of whether the evidence should be admitted under the good-faith exception to the exclusionary rule was not raised in the trial court, and therefore is not appropriately before us. See A.O. Smith Harvestore Prods., Inc. v. Kallsen, 817 P.2d 1038 (Colo.1991); Alzado v. Blinder, Robinson & Co., 752 P.2d 544 (Colo.1988).
*153Y.
The ruling of the trial court suppressing the evidence seized at Titus’ residence is affirmed.
SCOTT, J., concurs. MULLARKEY, J., dissents, and ROYERA, C.J., and LOHR, J., join in the dissent.. § 18-18-406(8), 8B C.R.S. (1993 Supp.).
. § 18-18-406(4), 8B C.R.S. (1993 Supp.).
. The tape recording was not considered by the judge who suppressed the evidence and is not a part of this appeal. We rely on Detective Richter’s affidavit for a summary of the conversation, but also recognize that the defendant's brief to this court asserts that the affidavit does not accurately relate the conversation that took place between Titus and the informant.
. Titus could have raised, but did not, the issues of stale information in the affidavit or stale probable cause. Although the officer did not apply for the warrant until October 15, he had received the report of the anonymous informant in July, performed his surveillance in August, and had attempted to stage the sale of marijuana on August 22. We draw no conclusions on the staleness issue.