David Sherbrooke filed this action pursuant to 42 U.S.C. § 1983, claiming that the City of Pelican Rapids, Minnesota, and several of its police officers violated his constitutional rights. Specifically, Sher-brooke alleged that the officers violated his rights under the Fourth Amendment by stopping his car without probable cause and by recording one side of a conversation between Sherbrooke and his attorney. Sherbrooke also claimed that the officers committed several violations of state law, and alleged that the city was liable for maintaining an unconstitutional policy.
The district court dismissed most of Sherbrooke’s claims, but denied the defendants’ motion for summary judgment on the claim relating to the traffic stop. The court also granted summary judgment for Sherbrooke on the claim concerning the recording of his statements during a telephone call with his attorney. The police officers and police chief appeal the district court’s denial of qualified immunity, and the city appeals the court’s denial of its motion for summary judgment. We reverse and remand.
*812I.
On the night of July 24, 2004, Sher-brooke attended a high school class reunion at the Veterans of Foreign Wars hall in Pelican Rapids. At the reunion, Sher-brooke drank several alcoholic beverages before driving his pickup truck back to his lake house at about 12:25 a.m. Along the way, Sherbrooke pulled over to the side of Minnesota Highway 59 to look up a telephone number. While parked along the side of the highway, Sherbrooke activated his hazard lights to alert passing traffic that he had pulled over.
After finding the telephone number and completing a telephone call, Sherbrooke pulled away from the shoulder and continued driving down the highway. Sher-brooke testified that a police vehicle was parked at a stop sign “about 1,100 feet” up the road and around a bend from where Sherbrooke had pulled over. Officer Scott Sachs was in the squad car, performing patrol work. Sherbrooke testified that he turned off the hazard lights when his vehicle reached the 55 mile-per-hour speed limit, which, he says, “is the correct way to do it.” At the same time, Sherbrooke conceded that he turned his hazard lights off about 200 yards before reaching Sachs’s police vehicle, and only after noticing that Sachs’s car was a police vehicle. Upon seeing the police vehicle, Sherbrooke gathered his thoughts, cheeked his speed, and noticed that his hazard lights remained on.
After seeing Sherbrooke drive by, Officer Sachs pulled out behind Sherbrooke, followed him for about twenty-five seconds, and then signaled to Sherbrooke to pull over. Sherbrooke testified that by the time Officer Sachs pulled him over, the hazard lights had been deactivated. After pulling to the side of the road, Sherbrooke got out of his truck, but Officer Sachs ordered him back into the vehicle. Sher-brooke testified that Sachs then waited four minutes before approaching Sher-brooke’s truck. Sherbrooke later alleged that he was pulled over because Sachs was involved in a contest with other officers to see who could make the most arrests for driving while intoxicated.
During the traffic stop, Officer Sachs detected alcohol on Sherbrooke’s breath and looked for signs of impairment. After conducting a series of field sobriety tests and a portable breath test, Sachs arrested Sherbrooke for drunk driving and transported him to the police department for additional testing.
At the police station, Sherbrooke consented to another, more accurate breath test called an Intoxilyzer. Pursuant to the standard operating procedure of the police department, Sherbrooke remained under video and audio surveillance so that the officers could monitor his food and water intake prior to administering the test. During the wait, Sherbrooke called his attorney and spoke to him while Sachs and another officer (defendant Ted Leabo) remained in the room. After speaking to his attorney, Sherbrooke took the Intoxilyzer test, which revealed that his blood alcohol level exceeded the legal limit for driving. Sherbrooke contends that Sachs caused Sherbrooke to drink warm water before the test, and then improperly administered the test, thus resulting in an artificially high reading. Sherbrooke then requested a blood test. The blood test, administered at a nearby hospital, was not admissible in court. The charges against Sherbrooke eventually were dropped, and he was never prosecuted.
Sherbrooke brought this suit for damages, alleging violations of his constitutional rights, as well as “mental anguish, pain and suffering and humiliation.” The district court dismissed most of his claims, but denied the defendants’ motion for summary judgment on Sherbrooke’s claim that *813the initial traffic stop was an unlawful seizure. The court also granted summary judgment for Sherbrooke on his claim that the officers unlawfully récorded one side of the telephone conversation with his attorney. The officers and the city filed this interlocutory appeal.
II.
As a preliminary matter, Sher-brooke challenges our jurisdiction over this appeal. We have jurisdiction to consider-an interlocutory appeal of an order denying qualified immunity to the extent the appeal seeks review of “purely legal determinations made by the district court.” Wilson v. Lawrence County, Mo., 260 F.3d 946, 951 (8th Cir.2001). We do not have jurisdiction to consider “which facts a party may, or may- not, be able to prove at trial,” Johnson v. Jones, 515 U.S. 304, 313, 115 S.Ct. 2151, 132 L.Ed.2d 238 (1995), but the city and the police officers do not bring this sort of fact-based appeal. Their contention is that even taking the facts in the light most favorable to Sherbrooke, neither the traffic stop nor the recording of Sherbrooke’s statements violated Sher-brooke’s clearly established rights under the Fourth Amendment. This is a purely legal question over which we have jurisdiction. See Saucier v. Katz, 533 U.S. 194, 201, 121 S.Ct. 2151, 150 L.Ed.2d 272 (2001); Dible v. Scholl, 506 F.3d 1106, 1109 (8th Cir.2007). We also have jurisdiction to consider the district court’s grant of partial summary judgment in favor of Sherbrooke, because it turns on the very same legal issue as the denial of qualified immunity—that is, whether the recording of Sherbrooke’s conversation with his attorney violated the Fourth Amendment. See Smith v. Ark. Dept. of Correction, 103 F.3d 637, 650 (8th Cir.1996). And we have jurisdiction to consider the City’s appeal of the denial of summary judgment on Sher-brooke’s allegation that a municipal policy caused a violation of his constitutional rights, because the merits of the City’s appeal is inextricably intertwined with the question whether the officers violated Sherbrooke’s rights. Smook v. Minnehaha County, 457 F.3d 806, 813 (8th Cir.2006), cert. denied, — U.S. —, 127 S.Ct. 1885, 167 L.Ed.2d 386 (2007).
In assessing a claim of qualified immunity, we are required first to ask whether the plaintiffs allegations establish a violation of the Constitution. Saucier, 533 U.S. at 201, 121 S.Ct. 2151. If so, then we “ask whether the right was clearly established” at the time of the violation. Id. “To defeat a claim of qualified immunity, the contours of an alleged constitutional right must be ‘sufficiently clear that a reasonable official would understand that ’ ” Smook, 457 F.3d at 813 (quoting Anderson v. Creighton, 483 U.S. 635, 640, 107 S.Ct. 3034, 97 L.Ed.2d 523 (1987)).
Sherbrooke’s first claim at issue on appeal is that Officer Sachs violated the Fourth Amendment by stopping Sher-brooke’s truck. Sachs argues that the seizure was constitutional because an objectively reasonable officer could have stopped the vehicle either to exercise a community caretaking function, see Cady v. Dombrowski, 413 U.S. 433, 441, 93 S.Ct. 2523, 37 L.Ed.2d 706 (1973), or to investigate a traffic violation for which there was probable .cause. As to the latter, probable cause that a driver has committed any traffic violation, no matter how minor, provides sufficient justification under the Fourth Amendment to stop a vehicle. Atwater v. City of Lago Vista, 532 U.S. 318, 354, 121 S.Ct. 1536, 149 L.Ed.2d 549 (2001). The officer’s subjective motivation is irrelevant. Brigham City v. Stuart, 547 U.S. 398, 126 S.Ct. 1943, 1948, 164 L.Ed.2d 650 (2006). Even if the officer was influenced by an impermissible motive, a traffic stop does not violate the driver’s rights under the Fourth Amendment to be free *814from unreasonable seizures, as long as the circumstances, viewed objectively, justified the seizure. Id,.; Whren v. United States, 517 U.S. 806, 813, 116 S.Ct. 1769, 135 L.Ed.2d 89 (1996).
Minnesota law prohibits the use of flashing lights on a vehicle except in limited circumstances, including “as a means of indicating, a right or left turn, or the presence of a vehicular traffic hazard requiring unusual care in approaching, overtaking, or passing.” Minn.Stat. § 169.64. Sher-brooke contends that his use of the flashers on his truck was permissible under the quoted exception, because he used his lights as a proper means of indicating that his vehicle presented a “vehicular traffic hazard.” His rationale is that when a , vehicle enters a roadway from a stopped position on the shoulder, the vehicle presents a vehicular traffic hazard until such time as the vehicle reaches the speed limit (in this case, fifty-five miles per hour), and that use of the flashers is thus permissible until that speed is attained.
We disagree with Sherbrooke’s interpretation of the Minnesota statutes. The posted speed limit is evidence of only the maximum speed that is reasonable and prudent on a roadway. Minn.Stat. § 169.14(2). There is no legal requirement that a vehicle' ever reach that speed. Vehicles may operate lawfully at reasonable and prudent speeds below the maximum without constituting a vehicular traffic hazard. Assuming Sherbrooke is correct that a vehicle may lawfully use its flashers to indicate a traffic hazard when the vehicle first enters a roadway in Minnesota, use of the flashers should cease when the vehicle reaches a speed that no longer presents a hazard. A reasonable officer surely could believe that speeds close to, but less than, the maximum posted limit present no traffic hazard. Sherbrooke concedes that he was using his flashers until he reached the maximum speed limit of fifty-five miles per hour. Because the speed of the vehicle during the preceding moments, when the vehicle was traveling slightly under the speed limit, presented no apparent traffic hazard, Officer Sachs had probable cause to stop Sherbrooke for improper use of flashing lights. We think the alternative interpretation of the statute apparently endorsed by the partial dissenting opinion—that highway drivers may use flashing lights whenever accelerating from reasonable and prudent speeds below the maximum (say, fifty to fifty-four miles per hour) up to the speed limit of fifty-five , miles per hour—more nearly “defies common sense” than does ours. Cf. post at 818-19.
Alternatively, even accepting Sherbrooke’s ihterpretation of the statutes for the sake of argument, we conclude that an objectively reasonable officer in Sachs’s position had probable cause to stop Sher-brooke’s truck for improper use of flashing lights. It is undisputed that Sachs did not observe Sherbrooke at the point when he was stopped at the side of the road to use the telephone before pulling back on to Highway 59. By Sherbrooke’s own testimony, the distance from where Sherbrooke pulled off the road to Sachs’s location was 1,100 feet, but Sherbrooke could not observe Sachs (and vice-versa) until after Sherbrooke came around a curve on the highway, at a distance between 600 and 900 feet from Sachs’s squad car. (Sher-brooke Dep. 59, Appellant’s App. A-33). Thus, even assuming it was permissible for Sherbrooke to operate his flashers from the time he reentered the highway until his vehicle reached fifty-five miles per hour, and even assuming any reasonable officer would have been expected to know that interpretation of the statute was correct, a reasonable officer in Sachs’s position would not have known that Sher-brooke recently reentered the roadway. From his location, Sachs simply observed *815Sherbrooke’s vehicle come around the curve with its flashing lights activated. A reasonable officer in those circumstances had probable cause to believe that Sher-brooke was in violation of the prohibition on flashing lights in Minn.Stat. § 169.64, because there was no apparent vehicular traffic hazard. Even if Sherbrooke, unbeknownst to Sachs, actually was using his flashers to alert other drivers after reentering the road from a stopped position, a law enforcement officer does not violate the Fourth Amendment if he seizes a suspect under the reasonable, but mistaken, belief that the suspect committed an offense. United States v. Smart, 393 F.3d 767, 770 (8th Cir.2005).
For these reasons, we conclude that Officer Sachs had probable cause to stop Sherbrooke for improper use of flashing lights. Accordingly, Sachs did not violate Sherbrooke’s constitutional rights under the Fourth Amendment, and Sachs’s motion for summary judgment on this point should have been granted. In view of our conclusion regarding probable cause, we need not consider whether the seizure also was justified by the officer’s exercise of his community caretaking function.
Sherbrooke’s second claim at issue on appeal relates to his telephone call to his attorney while in custody. The police in Pelican Rapids had a standard operating procedure of making an audio and video recording of detainees who were awaiting an Intoxilyzer test, with the stated purpose of preventing any action that would call into question the validity of the ensuing test. The officers investigating Sher-brooke activated the recording equipment in accordance with this procedure, so Sher-brooke’s speech was recorded while he was in the police station. Before taking the breath test, while in the presence of Officers Sachs and Leabo, Sherbrooke called his attorney to ask for legal advice. Sher-brooke’s end of this telephone call was recorded by the equipment that was already activated.
The district court held that the act of recording Sherbrooke’s speech during the telephone conversation with his attorney was an unconstitutional search. We disagree, because Sherbrooke had no reasonable expectation of privacy in what he said during this call. “What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection.” Katz v. United States, 389 U.S. 347, 351, 88 S.Ct. 507, 19 L.Ed.2d 576 (1967). Sherbrooke placed this telephone call in an open room, in which the presence of police officers was open and obvious. The tape recording even shows that Sherbrooke acknowledged, near the end of the conversation, that his statements were being recorded, and that this was “fine” with him. Under these circumstances, Sherbrooke could not reasonably expect that the conversation was private, and there was no search within the meaning of the Fourth Amendment. See United States v. Hatcher, 323 F.3d 666, 674 (8th Cir.2003); United States v. Gann, 732 F.2d 714, 723 (9th Cir.1984). That communications between an attorney and client generally are privileged when conducted privately does not mean that a conversation knowingly conducted in the presence of others is privileged or private. Sherbrooke’s contention that the police allegedly prevented him from placing a private call to his attorney is properly addressed, if at all, under constitutional provisions other than the Fourth Amendment. Cf. Friedman v. Comm’r of Public Safety, 473 N.W.2d 828, 835 (Minn.1991).1
*816The City’s appeal is inextricably intertwined with the appeal of the police officers. Because the police officers did not violate Sherbrooke’s constitutional rights under the Fourth Amendment, there can be no municipal liability under the Fourth Amendment for an unconstitutional policy. McCoy v. City of Monticello, 411 F.3d 920, 922 (8th Cir.2005). Accordingly, the City is also entitled to summary judgment on that claim.
For the foregoing reasons, we reverse the district court’s orders denying the officers’ motions for summary judgment based on qualified immunity, denying the City’s motion for summary judgment, and granting in part Sherbrooke’s motion for summary judgment. The case is remanded for further proceedings consistent with this opinion.
. Sherbrooke also alleged that the recording violated his rights under the Fifth and Sixth Amendments to the Constitution of the United States, but the district court dismissed those claims.