Skip to content


By: Chase Slasinski, Volume 106 Staff Member

The use of dogs in policing is a practice that has existed in the United States for over a century.[1] Countless searches and seizures have been predicated on dogs’ detection of the faintest odors of illegal drugs, explosives, and other contraband items. In the context of vehicle searches for illegal narcotics, the Supreme Court has established that a police dog’s “alert” to the presence of contraband is sufficient to establish the level of reasonable suspicion necessary to conduct the search.[2]

However, the issue of what type of behavior constitutes an “alert” is one that is largely unexamined in our jurisprudence.[3] In the case of U.S. v. Braddy, the Eleventh Circuit confronted the question of whether a change in a dog’s behavior, rather than its “final response” to the presence of contraband, was sufficient to establish probable cause.[4] As the court explains, the drug dog “gave a ‘canine alert’ by leaning its body forward, closing its mouth, and changing its breathing and body posture, with the dog’s tail becoming erect. The dog, however, was unable to go into its trained “final response,” (its final alert) as it was not able to directly pinpoint the odor.”[5] This response was not the dog’s trained reaction, but the court accepted that the behavior observed was sufficient to establish probable cause, as the handler had seen this response “on ‘many’ occasions, and because it was consistent with the dog’s behavior during training.”[6] The officer explained that he was trained to look for the dog’s “‘change in body posture and a change in breathing’ leading to the dog’s paw scratch as a ‘final response.’”[7]

The probable cause inquiry, according to the court, requires a flexible assessment of the facts surrounding a dog’s alert,[8] considering the totality of the circumstances viewed through the lens of a reasonably prudent person.[9] The court held that the officer’s observation of an “odor response” alone was enough. However, the factual circumstances involved in Braddy mirrored those in the Fifth Circuit case U.S. v. Rivas.[10] There, the court held that a drug dog’s “casting” or “weak alert” was “too distantly related to an alert to create reasonable suspicion . . . as a matter of law.”[11] The Fifth Circuit is an outlier in this regard,[12] but its conclusion (though minimally analyzed) is consonant with the values inherent in the Fourth Amendment.


As one commentator notes, “virtually all handlers will represent that their canine alerted in connection with [a] contraband find, [and] their conclusions continue to enjoy total deference by trial courts.”[13] Even so, there is little agreement among courts regarding the definition of an alert.[14] The terminology varies, with some courts describing an alert as either an “aggressive” or “passive” response,[15]  while other courts have regarded an alert as behavior that nears these final responses, but nevertheless does not constitute the full indication the dog was trained to perform.[16] The behavior at issue in Braddy was closer to this latter type, and in relying on the officer’s observations of the dog’s less-than-final odor response, the court was satisfied that probable cause was established by this indication along with evidence of the dog’s training and handler’s experience.[17] The problem with this conclusion is twofold: firstly, the analysis seems to assume that since the handler calls the dog’s response an “alert” it is one, and relatedly, the court does not scrutinize the handler’s interpretations of subtle and ambiguous changes in dog behavior, placing more reliance on the officer’s subjective interpretations rather than the objective facts[18] necessary to establish probable cause.


There is a widespread perception that drug sniffs are reliable indicators of the presence of narcotics, often ignoring errors and biases inherent in the handler-canine dynamic. Trial courts have often considered certification of a dog’s training and certification to be dispositive in determining reliability,[19] and the dog and handler’s experience in the field has been seen as an additional plus factor.[20] Moreover, the Supreme Court has emphasized the sui generis nature of the sniffs,[21] regarding them as highly accurate tools of law enforcement.[22] But the “theory of the infallible drug dog”[23] is problematic for several reasons. Firstly, even in circumstances where a drug dog performs its “final alert,” there is still a common risk that the canine has falsely alerted to the presence of a legal substance,[24] leftover residue of an illegal substance,[25] or no substance at all. For example, there are many prescription drugs containing opioid compounds which, when exposed to air, have the same distinctive odor given off by heroin.[26] These odors are indistinguishable even to a highly trained drug dog.[27] Moreover, there is often little attention paid to the rates of false-negatives and false-positives rates for individual dogs,[28] with various courts accepting accuracy rates far lower than 90%.[29]


Just as drug canines are not perfect at detecting the presence of narcotics, handlers often misidentify the reactions from their canines[30] or bias the dog’s response via their own behavior.[31] It’s not enough for an officer to claim that they “know their dog”[32] or represent that repeated behavior exhibited in training and in the field establishes a baseline level of reliability[33] for purposes of establishing probable cause. Although experience and training are factors that should be considered in determining the accuracy of the response, something less than a trained and repeated response opens the door to relying on the “subjective good faith”[34] of the officer rather than the positive and verifiable indication from a “well-trained” dog[35] (i.e., a final alert).


Given the risk of error already present in interpreting the more distinctive responses of drug canines, the possibility of error is magnified in relying on dog behavior that is less than evident. Although evaluating the reliability of drug canines involves a fact-intensive inquiry that does not require a “strict evidentiary checklist,”[36] the Fourth Amendment is grounded in making objective determinations based on specific and articulable facts.[37] The Court has accepted the fact that the canine and handler may stand in for the neutral and detached magistrate[38] because they are “highly trained tool[s] of law enforcement, geared to respond in distinctive ways to specific scents so as to convey clear and reliable information to their human partners.”[39] The distinctive nature of a dog’s response can only be properly determined by relying on trained cues that are detectable by the officer and can be easily verified by a finder of fact. Relying on an officers’ interpretations of other behavioral changes supplants the officer’s opinion and educated guesses for those specific articulable facts necessary to establish probable cause. Therefore, the conclusion in Rivas is not surprising and may signal that this issue is ripe for reevaluation. By requiring final alerts, courts may satisfy the minimum quantum of evidence necessary to establish probable cause without risking an excessive likelihood of error.


[1] William Handy, Marilyn Harrington & David J. Pittman, The K-9 Corps: The Use of Dogs in Police Work, 52 J. Crim. L. & Criminology 328, 329 (1961).

[2] Florida v. Harris, 568 U.S. 237, 246–48 (2013).

[3] Jorge G. Aristotelidis, Trained Canines at the U.S.-Mexico Border Region: A Review of Current Fifth Circuit Law and a Call for Change, 5 Sch. St. Mary’s L. Rev. Minor Issues 227, 230 (2002).

[4] United States v. Braddy, 11 F.4th 1298, 1312–15 (11th Cir. 2021).

[5] Id. at 1304.

[6] Id. at 1313.

[7] Id.

[8] Id. at 1312; see also Harris, 568 U.S. at 244 (quoting Illinois v. Gates, 462 U.S. 213, 231, 238 (1983)) (noting that determining probable cause is a flexible, all-things-considered approach, turning on the assessment of probabilities in particular factual contexts).

[9] Braddy, 11 F.4th at 1312.

[10] Similar to the partial response in Braddy, the dog in Rivas “casted” to the presence of narcotics. United States v. Rivas, 157 F.3d 364, 367–68 (5th Cir. 1998). The handler explained that “‘casting’ is in a sense the dog maybe feels not a strong alert, but something that temporarily stops him and deters his attention at that point. And although he doesn’t pursue as aggressive alert, he does stop and give it minute attention and continues with his duties by continuing his examination.” Id. at 368.

[11] Id.

[12] Aristotelidis, supra note 3; Lewis R. Katz & Aaron P. Golembiewski, Curbing the Dog: Extending the Protection of the Fourth Amendment to Police Drug Dogs, 85 Neb. L. Rev. 735, 764 (2006).

[13] Aristotelidis, supra note 3.

[14] Jeffrey S. Weiner & Kimberly Homan, Those Doggone Sniffs Are Often Wrong: The Fourth Amendment Has Gone to the Dogs!, 30-APR Champion 12, 13 (2006).

[15] The court in United States v. Johnson, 323 F.3d 566, 567 (7th Cir. 2003) explains the distinction, noting that a dog trained to alert aggressively tries to contact the scent source (biting, scratching, penetrating, attempting to retrieve), while the dog that alerts passively does not try to contact the scent source but instead performs trained behavior (sitting, looking at the source, sniffing toward the source, looking at the handler).

[16] See United States v. Parada, 577 F.3d 1275, 1282 (10th Cir. 2009) (holding that it was not necessary for the drug dog to alert to the source of the odor); United States v. Diaz, 25 F.3d 392, 394-95 (6th Cir. 1994) (accepting testimony from the officer that the dog would occasionally alert by coming to a standstill instead of alerting by his normal aggressive response); United States v. Trayer, 898 F.2d 805, 808 (D.C. Cir. 1990) (finding that despite the fact that the dog did not perform its aggressive trained response, its pointing to the source of the odor was sufficient to establish probable cause); United States v. Outlaw, 134 F.Supp.2d 807, 813 (W.D. Tex. 2001) (“[A]n alert is simply an interpretation of a change in the dog’s behavior by a human handler.”); see also United States v. Bartz, 2004 WL 1465780, at *5 (S.D. Ind. June 25, 2004) (noting that a handler’s training includes learning how to recognize the changes in dog’s behavior signaling the detection of narcotics).

[17] United States v. Braddy, 11 F.4th 1298, 1312–15 (11th Cir. 2021).

[18] Probable cause requires the officer to “be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion.” Terry v. Ohio, 392 U.S. 1, 21 (1968); see also United States v. Tapia, 912 F.2d 1367 (11th Cir. 1990) (quoting United States v. Sokolow, 490 U.S. 1, 7 (1989) (“‘[R]easonable suspicion’ must be more than an inchoate ‘hunch,’ and the fourth amendment accordingly requires that police articulate some minimal, objective justification for an investigatory stop.”). But see Outlaw, 134 F.Supp.2d at 813 (“[A] canine alert is not always an objectively verifiable event.”).

[19] See, e.g., United States v. Sentovich, 677 F.2d 834, 838 n.8 (11th Cir. 1982) (accepting an affidavit that the dog was trained in drug detection as singularly sufficient to establish reliability); United States v. Berry, 90 F.3d 148, 153 (6th Cir. 1996) (accepting sufficiency of affidavit that dog was trained and qualified to conduct drug searches); United States v. Daniel, 982 F.2d 146 (5th Cir. 1993) (accepting sufficiency of affidavit that dog was trained to detect presence of narcotics).

[20] See, e.g., United States v. Pore, 328 F.Supp.2d 591, 595 (D. Md. 2004) (finding it unlikely that handler would misinterpret dog’s behavior because handler and dog had worked together for a year); State v. Ellison, 455 So.2d 424, 431 (Fla. Dist. Ct. App. 1984) (considering an officer’s knowledge and expertise as relevant to the inquiry); State v. Litke, 846 N.W.2d 34 (Ct. App. Wis. 2014) (considering years served by the handler-dog team and number of stops as sufficient to find probable cause).

[21] Illinois v. Caballes, 543 U.S. 405, 409 (2005) (quoting United States v. Place, 462 U.S. 696, 707 (1983)). The sui generis label rests partially upon the fact that dog sniffs are reliable and “generally likely, to reveal only the presence of contraband.” Id.; Place, 462 U.S. at 707; Katz & Golembiewski, supra note 12, at 774.

[22] Katz & Golembiewski, supra note 12, at 737.

[23] Caballes, 543 U.S. at 411 (Souter, J., dissenting) (“[T]he infallible dog . . . is a creature of legal fiction.”); see also Weiner & Homan, supra note 14, at n.7 (describing how the entrenched myth of the infallible drug dog relies in part on the perception that dog’s sniffs are uniquely calibrated to reveal only the presence of contraband).

[24] See infra note 25.

[25] See, e.g., United States v. $242,484.00, 351 F.3d 499, 511 (11th Cir. 2003) (noting that because as much as 80% of all currency in circulation contains drug residue, a dog alert “is of little value”); United States v. Carr, 25 F.3d 1194, 1214–1217 (3d Cir. 1994) (“[A] substantial portion of United States currency . . . is tainted with sufficient traces of controlled substances to cause a trained canine to alert to their presence.”).

[26] Katz & Golembiewski, supra note 12, at 754.

[27] Id.

[28] See, e.g., United States v. Hill, 195 F.3d 258 (6th Cir. 1999) (finding that a handler’s failure to keep data on false alerts did not suggest the dog was unreliable); United States v. Diaz, 25 F.3d 392 (6th Cir. 1994) (finding that a lack of testimony regarding the dog’s searches and rate of success was not dispositive).

[29] See, e.g., United States v. Kennedy, 131 F.3d 1371, 1378 (10th Cir. 1997) (describing a dog that had a 71% accuracy rate); United States v. Scarborough, 128 F.3d 1373, 1378, n. 3 (10th Cir. 1997) (describing a dog that erroneously alerted 4 times out of 19 while working for the postal service and 8% of the time over its entire career); United States v. Limares, 269 F.3d 794, 797 (7th Cir. 2001) (accepting as reliable a dog that gave false positives between 7% and 38% of the time).

[30] See Katz & Golembiewski, supra note 12, at 763 (explaining that handlers may misinterpret dog’s signals given natural limitations to the dog’s ability to sniff effectively, such as sitting (a passive alert) when the dog is fatigued).

[31] See id. (explaining that dogs are extremely sensitive to handler’s reactions, such as when the officer alters their body posture and breathing when they suspect drugs may be present); see also Diaz, 25 F.3d at 396 (suggesting that “cueing” may jeopardize the reliability of dog sniffs); United States v. Outlaw, 134 F.Supp.2d 807, 813 (W.D. Tex. 2001) (explaining that a false alert can result from a handler’s conscious or unconscious signals).

[32] See Aristotelidis, supra note 3, at 231 (“Educated guesses based upon the handler’s knowledge of their dog’s training and past performance are nothing more than educated guesses when their dog fails to make the defined final response during a specific search. . . . When a dog makes the defined final response and no target odors are found on physical search one must rely on forensic chemical analysis to justify the accuracy of the dog.”).

[33] See id. (“The handler may assume any response other than the defined final response verifies the presence of a target odor. A [sic] this point the handler is guilty of interpretation, supposition, or speculation.”); Weiner & Homan, supra note 14, at 14 (“If the dog gave any other response, then it was not doing what it was trained to do, and there is sound reason to question whether an alert did in fact take place.”).

[34] See United States v. Wilson, 995 F.Supp.2d 455, 475 (W.D. N.C. 2014) (“To allow a search predicated upon an officer’s interpretation of the utterly minimalist lesser showing exhibited by the dog in this case would be tantamount to permitting law enforcement officers to issue their own search warrants based upon their own subjective analysis, something the Framers explicitly prohibited.”); cf. Beck v. Ohio, 379 U.S. 89, 97 (1964) (“If [an officer’s] subjective good faith alone were the test, the protections of the Fourth Amendment would evaporate, and the people would be ‘secure in their persons, houses, papers, and effects,’ only in the discretion of the police.”); Whren v. United States, 517 U.S. 806, 812–13 (1996) (noting that subjective motives and beliefs of an officer are irrelevant to a finding of probable cause).

[35] See United States v. Heir, 107 F.Supp.2d 1088, 1097 (D. Neb. 2000) (noting that objectively observable behavior, i.e., “indication” behavior, must be established in connection with proof of adequate training).

[36] United States v. Braddy, 11 F.4th 1298, 1312 (11th Cir. 2021) (quoting Harris, 568 U.S. at 244–45).

[37] See supra note 18; United States v. Boyce, 351 F.3d 1102, 1107 (11th Cir. 2003).

[38] See generally Illinois v. Gates, 462 U.S. 213, 236 (1983) (noting the strong preference for searches conducted pursuant to a warrant from a neutral detached magistrate).

[39]  Florida v. Jardines, 569 U.S. 1, 12–13 (2013).