PUBLISH UNITED STATES COURT OF APPEALS FOR THE TENTH CIRCUIT

_________________________________ MARISELA AGUILAR; MIGUEL BLANCO; FRANCISCO J. CARRANZA; RAFAEL GALLEGOS; BENJAMIN GUERRERO, JR.; VA UGHN D. HAYES, SR.; JOSE R. HERNANDEZ; ROGELIO HERNANDEZ; ROMAN JAUREGUI; EFREN JIMENEZ; FLAVIO LARA; SIXTO NAVARRETE; ANTHONY GUADALUPE ORDAZ; ARMANDO PACHECO, JR.; ALAN PEREZ; RIGOBERTO RODARTE; ANTONIO VASQUEZ; ADRIAN VILLALOBOS, a/k/a Jose Adrian Villalobos; MARIA ACEVEDO; ANGEL AGUILAR; EZEQUIEL ALVARADO; RICARDO ANGULO; FERNANDO APODACA; RENE ARREOLA; ANNETTE BAEZA; JUAN BAEZA; REYMUNDO BALDERRAMA; JUSTIN BARBA; RAMON BAXTER; STEPHANIE BERTOLLI; PEDRO BLANCO; DANIEL BOADO; ANTHONY CALLA; LESLIE CAMARILLO; YOLANDA CAMPOS; STEFANY CARRANZA; JENNIFER COOPER; EDWARD DANG; LUIS DORADO; LUZ DUARTE; MIGUEL DUENAS; JIM ESCALERA; HIRAM ESCOBAR; JAIME ESCOBAR; MARTIN L. ESPINOSA; CAROLINA ESTRADA; GUADALUPE ESTRAD A; CHRISTINE FIERRO; JOSE FUEN TES; MICHELLE GALLEGOS; ALBERT GARCIA; ANTHONY GARCIA; ARTURO GARCIA; EDWARD GARCIA; CAESAR GONZALEZ; JUAN GONZALEZ; RAUL GUZMAN; DAVID HERNANDEZ; No. 17-2198 FILED United States Court of Appeals Tenth Circuit 

### February 4, 2020 Christopher M. Wolpert Clerk of Court2 JESUS HERNANDEZ; PAUL HERNANDEZ; GINO HIJAR; JUN KOO; ROCIO D. LEZA; CHRISTOPHER MACIAS; ANGEL MALDONADO; ARTURO MARES; DANIEL MARQUEZ; PEDRO MARTINEZ; SAUL MARTINEZ; YVONNE MARTINEZ; JUAN MATAMOROS; YARETH MIRELES; GABRIEL MOLINA; ARTURO MONTERO; CARLOS MONTESINOS; CECILIA MORALES; JESUS MORALES; YVETTE MOREHEAD; NORMA MUNIZ; SANDRA NERIA; HERNAN NEVAREZ; ERICA NIETO; ERIK ONTIVEROS; GARY LEE OROZCO; LUIS ORTIZ; ROBERT ORTIZ; DAVID PADILLA; JUAN PARRA; VERONICAPENA; CARLOS PONCE; JORGE PORTILLO; OSCAR PORTILLO; JOSE I. PROSPERO; ISELA QUEZADA; EDGAR RAMIREZ; MIGUEL RAMIREZ; YGNACIO RAMIREZ; GUSTAVO RAMON; RODOLFO RINCON, SR.; RODOLFO RINCON, JR.; ALBERTO RIVERA; JENNIFER RIVERA; DANIEL RODRIGUEZ; OSCAR RODRIGUEZ; RUBEN RODRIGUEZ; VINCE ROMAN; CARLOS ROSALES; ABEL SAENZ; LILA SAENZ; BELINDA SANCHEZ; DAVID SANCHEZ; ABRAHAM SANDOVAL; GABRIELA SIFUENTES; SALVADOR SIFUENTES; IRMA SOTO; IRENE TERRAZAS-RUBIO; MANUEL VASQUEZ; ADRIANA VILLALOBOS; KARINA VILLALOBOS; SASHA VILLALVA; MEAGAN VILLIGAN, Plaintiffs - Appellants,

v. MANAGEMENT & TRAINING3 CORPORATION, d/b/a MTC, Defendant - Appellee.

_________________________________ Appeal from the United States District Court for the District of New Mexico (D.C. No. 2:16-CV-00050-WJ-GJF)

_________________________________ John P. Mobbs, El Paso, Texas, for Plaintiffs-Appellants. Aaron C. Viets, Rodey, Dickason, Sloan, Akin & Robb, P.A., Albuquerque, New Mexico (Charles J. Vigil, with him on the brief), for Defendant-Appellee.

_________________________________ Before BACHARACH , EBEL , and MORITZ , Circuit Judges.

_________________________________ MORITZ , Circuit Judge.

_________________________________ A group of 122 detention officers (the o fficers) who work or worked at Otero County Prison near Chaparral, New Mexico, allege that their employer, Management & Training Corporation (MTC), fails to pay them for cer tain activities that they engage in before they arrive at, when they arrive at, and after they leave their posts within the prison. According to the officers, these activ ities constitute compensable work, so MTC’s failure to pay violates bot h the Fair Labor Standards Act (FLSA) of 1938, 29 U.S.C. §§ 201–19, and the New Me xico Minimum Wage Act, N.M. Stat. Ann. §§ 50-4-1 to 50-4-33. 1

1 Below, the district court concluded th at the officers “c oncede[d] that if summary judgment was granted to their fede ral claims, it would also apply to the state law claims.” App. vol. 5, 1184. The officers take a different position on appeal, insisting that state and federa l law treat compensability diffe rently, such that even if4 As explained below, we conclude that in this context, these activities constitute compensable work. Fu rther, we reject MTC’s ar guments that (1) the time the officers devote to these activities is de minimis and (2) it need not pay the officers for these acti vities because it did not know th e officers were engaging in them. Additionally, we conclude that the officers’ rounding clai m survives summary judgment. As such, we reverse the distri ct court’s order awarding summary judgment to MTC and remand for further proceedings. Background The officers are “[r]espons ible for the custody and di scipline of detainees.” App. vol. 3, 573. Among other duties, th e officers “[s]earch for contraband and provide security”; “[c]ount, feed[,] and supervise detain ees in housing, work[,] and other areas”; and “prepare and mainta in records, forms[,] and reports.” Id. The officers generally work eight-h our shifts, five days a w eek. There are three shifts, beginning at 6 a.m., 2 p.m., and 10 p.m. Each officer is typically assigned to work his or her shift at a specific pos t, and there are more than 30 posts within the prison. Because this case concerns th e activities that the officers engage in before they arrive at and after they leav e their posts, as well as one activity at post, we begin by briefly outlining the officers’ undisputed daily routine. (We will later describe certain of these activities in gr eater detail, as necessa ry to our analysis.)

their federal claims fail, th eir state claims survive su mmary judgment. Because we ultimately find in the officer s’ favor under federal law, we need not address the officers’ argument on appeal or separate ly discuss their state-law claims.5 When the officers arrive at the prison, they in itially undergo a security screening. Then—in what the parties char acterize as a “pre[] shift briefing”—some officers receive post assignments from a su pervisor. App. vol. 5, 1158. During the preshift briefing, officers sometimes receive paperwor k or additional information about their post for that day. Next, some of ficers obtain the keys they need for the day’s post from a fingerprint-a ctivated box. And some or most officers collect any equipment they need for the day, such as handcuffs, a ra dio, or pepper spray, from the prison’s inventory-control system. The officers then walk to their posts, where they receive a “pass[]down br iefing” from the officer leav ing the post. Aplt. Br. 5. After working their shifts, de parting officers complete seve ral of the same tasks in reverse: they provide a pa ssdown briefing to an incoming officer, walk back from their post, and return their keys and equipment to the fi ngerprint-activated box and the prison’s inventory-cont rol system, respectively. 2 MTC requires the officers to use a time clock to precise ly record their arrival and departure times; officer s clock in after undergoing th e security screening and clock out after returning their keys and equipment. Nevertheless, MTC generally pays the officers based on their scheduled ei ght-hour shifts rather than on the precise times at which they clock in and out. Th e one exception to this policy is the tenminute adjustment rule: if an officer clocks in or out more than ten minutes before or

2The precise amount of time the officers devot e to these activities is disputed. The district court concluded that the offi cers devote no more than eight minutes per shift to completing these activ ities; the officers contend that the time exceeds ten minutes per day. But as we expl ain later, this dispute is notmaterial to our analysis.6 after his or her shift start or end time, MTC will pay the officer based on the time clock rather than on his or her scheduled shift. That is, if an officer clocks in for a 6 a.m. shift at 5:58 a.m. and clocks out at 2:09 p.m., MTC will pay that o fficer for the eight-hour shift (i.e., from 6:00 a.m. to 2:00 p.m.); but if an officer clocks in for that same shift at 5:45 a.m. and clocks out at 1:49 p.m., MTC will pay that officer based on the time clock (i.e., for eight hours and f our minutes). This rule applies on either end of the shift time, so that if an officer clocks in at 5: 49 a.m. and clocks out at 1:56 p.m., MTC will pay that officer for time wo rked from 5:49 a.m., the clock-in time, to 2 p.m., the shift-end time (i.e., for ei ght hours and 11 minutes). In addition, MTC provides officers with time-adjustment fo rms, which the officer s can complete to request payment if they devote time outside of their scheduled shift to compensable work. The officers contend that MTC’s comp ensation system deprives them of overtime pay in two ways. First, they alle ge that because MTC typically pays them based on shift time rather than clock time, it fails to pay themfor the time they devote to undergoing the security screening, receiving the preshift briefing, checking keys and equipment in and out, walking to and from post, a nd conducting passdown briefings. Second, the office rs allege that MTC’s te n-minute adjustment rule routinely rounds down their work time, resulting in systematic underpayment. Following discovery, MTC moved for summary judgment. It argued that officers do not perform comp ensable work under the FLSA when they undergo the security screening, receive the preshift briefing, check keys and equipment in and7 out, walk to and from post, and cond uct passdown briefings. Further, MTC alternatively argued that if any of that ti me was compensable, it was de minimis and thus not recoverable. See 29 C.F.R. § 785.47 (providing that “insubstantial or insignificant periods of time beyond the sc heduled working hours, which cannot as a practical administrative matte r be precisely recorded fo r payroll purposes, may be disregarded”). MTC additionally (1) insisted that it did not impermissibly round off the officers’ working time and (2) raised an estoppel defens e, arguing that it need not pay the officers because it did not know the o fficers were engaging in these activities. The district court ruled that of the ac tivities the officers described, only the passdown briefing was integral and indispensable to the o fficers’ principal activities and therefore compensable. But the distri ct court ultimately concluded the officers were not entitled to compensation for th e time devoted to conducting passdown briefings because that time wa s de minimis. It further re jected the officers’ rounding claim. As such, the district court gr anted MTC summary judgment on all of the officers’ claims (without r eaching MTC’s estoppel defens e). The officers appeal. Analysis “We review the district court’s summary[-]judgment decision de novo, applying the same standards as the district court.” Punt v. Kelly Servs. , 862 F.3d 1040, 1046 (10th Cir. 2017). “Under these standards, ‘[s]ummary judgment is proper if, viewing the evidence in th e light most favorable to th e non[]moving party, there is no genuine dispute as to any material fact a nd the movant is entitl ed to judgment as a8 matter of law.’” Id. (first alteration in original) (quoting Peterson v. Martinez , 707 F.3d 1197, 1207 (10th Cir. 2013)). I. Compensable Work The FLSA requires an employer to pay employees for their work, but it does not define what kinds of activiti es qualify as compensable work. See 29 U.S.C. §§ 206–07; Integrity Staffing Sol s., Inc. v. Busk , 574 U.S. 27, 31 (2014). Confronting that absence, the Supreme Court initially defined compensabl e work as “all time during which an employee is necessarily re quired to be on the employer’s premises, on duty or at a prescribed workplace.” Busk , 574 U.S. at 31 (quoting Anderson v. Mt. Clemens Pottery Co. , 328 U.S. 680, 690–6 91 (1946)). But Congress narrowed that definition when it enacted the Portal-to-Po rtal Act of 1947, 29 U.S.C. §§ 251–62, which carves out two exclusi ons from the FLSA’s defin ition of compensable work. See Busk , 574 U.S. at 32–33. First, the Act provides that the time an employee devotes to “walking, riding, or traveling to and from the actual place of performance of the principal activity or activities which such employee is employed to perform” is not compensable. 29 U.S.C. § 254(a)(1). Second, the Act provides that the time devoted to “activities which ar e preliminary to or postlimi nary to [the employee’s] principal activity or activities” is not compensable. § 254(a)(2). Determining whether an activity is “preli minary to or postliminary to . . . [a] principal activity or activities” requires deciding what constitutes an employee’s “principal activity or activities.” Id. Courts have defined th is phrase to include both the principal activities them selves and “all ac tivities which are an ‘integral and9 indispensable part of th e principal activities.’” Busk , 574 U.S. at 33 (quoting IBP, Inc. v. Alvarez , 546 U.S. 21, 29–30 (2005)); see also 29 C.F.R. § 790.8(b), (c). In turn, an activity is “integral and indispensable . . . if it is an intrinsic element of those [principal] activitie s and one with which the employee cannot dispense if [the employee] is to perform his [o r her] principal activities.” Busk , 574 U.S. at 33. Critically, the integral-and-indispensabl e inquiry does not turn on whether the employer requires the activity or whethe r the activity benefits the employer. 3 Id. at 36. Instead, the question is “tied to th e productive work that the employee is employed to perform .” Id. Here, the parties agree that the o fficers’ principal activities include maintaining “the custody and discipline of inmates,” “supervising detainees,” “searching for contraband[,] and providing security.” App. vol. 3, 446. But the officers argue that the dist rict court erred when it c oncluded that the officers’ activities before th ey reach their posts and afte r they leave th eir posts are

3 Before the Supreme Court decided Busk , courts routinely decided the integral-and-indispensable is sue by asking these two ques tions: whether the employer required the activity or whether th e activity benefited the employer. See, e.g. , Whelan Sec. Co. v. United States , 7 Cl. Ct. 496, 498–99 (1985). But the Busk court specifically rejected those a pproaches as “overbroad.” Busk , 574 U.S. at 36. Accordingly, Buskeffected a change in the la w. Thus, to the extent a pre- Buskcase turned on these now-disapproved rationales, its analysis of the integral-andindispensable issue is inapposite. See Bridges v. Empire Scaffold, L.L.C. , 875 F.3d 222, 227–28 (5th Cir. 2017) (rejec ting reliance on pre- Buskcases whose rationales were no longer applicable). Howeve r, to the extent that a pre- Buskcase did not turn on these now-disapproved rationales, it remains on point. So, throughout this opinion, we disclaim reliance on pre- Buskcases that turned on these nowdisapproved rationales but c ontinue to rely on pre- Buskcases that did not.10 noncompensable preliminary and postliminary activities th at are not integral or indispensable to these prin cipal activities. For the reas ons explained below, we conclude that all these activities—underg oing the security screening, receiving the preshift briefing, picking up and returning keys and equi pment, and walking to and from post—are integral and indispensable to the officers’ pr incipal activities. 4
A. Preshift Activities 5 We begin with the first act ivity of the officers’ day: the security screening. During the security screening—which occ upies between three and eleven minutes— the officers empty their pockets, remove their jackets and al l metal, sometimes remove their boots, present any briefcases, lunchboxes, or bags for inspection, and walk through a metal detector before re claiming their possessions. MTC requires and conducts the security screeni ng to ensure “the overall sa fety of the prison” and to prevent officers from inadvert ently or intentionally bri nging contraband like weapons or cell phones into the prison. App. vol. 3, 559. The district court determined that th e screening was “a preliminary security measure” that was not integral or indispen sable to the officers’ principal activities. App. vol. 5, 1158. In reaching this c onclusion, the district court relied on Busk , in

4 We also conclude, albeit for a different reason than the district court did, that the one activity occurring at post, the passdown briefi ng, is integral and indispensable to the office rs’ principal activities. 5 For ease of reference, we refer to the security screening, preshift briefing, key and equipment pickup, walk to post, an d preshift passdown br iefing as “preshift activities.” Likewise, we refer to the pos tshift passdown briefing, walk back from post, and key and equipment retu rn as “postshift activities.”11 which the Supreme Court held that a postshift security screening was not compensable under the FLSA. See 574 U.S. at 36. Buskinvolved warehouse employees whose job functi ons included “retriev[ing] products from warehouse shelves and packag[ing] thos e products for shipment.” Id. at 35. To deter theft, the employer required the employees to underg o a postshift security screening. Id. The Supreme Court held that the screening was not compensable work because it was not integral or indispensable to the employ ees’ principal activity of retrieving and packaging items from warehouse shelves. Id. In fact, the employer “could have eliminated the screenings altogether without impairi ng the employees’ ability to complete their work.” Id. But as the officers point out, Buskdid not hold that a s ecurity screening can never be compensable. Instead, the Court explained that whet her an activity is compensable depends on “the productive wo rk that the employee is employed to perform.” Id. at 36. And that “productive work ” marks the critical distinction between Buskand this case. Id. There, the theft-preven tion, postshift security screening was not “tied to” the work of retrieving items from warehouse shelves. Id. Indeed, there was no connection at all between the work and the screening. We cannot say the same here. MTC conduct s the security screening to prevent weapons and other contraband from enteri ng the prison. And keeping weapons and other contraband out of the prison is neces sarily “tied to” the officers’ work of providing prison security a nd searching for contraband. Id. Indeed, the security screening and the officers’ wo rk share the same purpose.12 MTC resists this connection, encouragin g us to adopt the district court’s reliance on Busk ’s suggestion that neither “searches conducted for the safety of the employees [nor] those conducted for the purpose of preventing theft” were integral or indispensable. Id. This statement in Busk concerned an opinion letter issued by the Department of Labor in 1951. Id. at 35. The Department’s letter explained that for employees in a rocket-powder plant, neither a preshift search aimed at preventing matches and cigarette lighters from entering the plant nor a postshift search aimed at preventing theft wa s compensable. Id. So, the Busk court reasoned, the Department drew no distinction between searches for employee safety and se arches to prevent theft. Id. at 35–36. But the Department based its opin ion letter on significantly different circumstances than those presented here . The screenings here are obviously not aimed at preventing theft. Neither are th ey necessarily anal ogous to the safety searches at the rock et-powder plant. And notably, neither the Department’s opinion letter nor the Court in Busk clearly outlined the principal activities of the employees at the rocket-powder plant. But the Busk Court explained that the plant’s preshift search was aimed at “the safety of employees.” Id. Standing on its own, an employer’s general desire to keep its employees safe has no clear or obvious connection to the particul ar activities those employees are employed to perform. Here, by contrast, the officers’ principal duties include “searching for contraband and providing security.” App. vol. 3, 446. So even if this securi ty screening relates in part to overall prison safety, what matters is that the screeni ng is “tied to” the productive13 work that MTC employs the officers to perform, rendering it integral and indispensable to those duties. 6 Busk , 574 U.S. at 36. Moreover, unlike the employer in Busk , MTC could not “have eliminated the screenings altogether wit hout impairing the employees’ ability to complete their work.” Id. at 35; see also id. at 37–38 (Sotomayor, J., concurring) (explaining that the question is whether employees “could not dispense with [the security screening] without impairing [their] abil ity to perform the[ir] princi pal activit[ies] safely and effectively”). Arguing against this conclu sion, MTC contends that an officer “can obviously maintain custody and discipline of inmates whether or not the officer walked through a metal detector earlier.” Ap lee. Br. 17. But indispensability does not depend upon whether the officers could perform some aspect of their jobs in the absence of the activity; the question is whether the empl oyer “could have eliminated the screenings altogether without impairi ng the employees’ ability to complete their work,” Busk , 574 U.S. at 35; see also id. at 37–38 (Sotomayor , J., concurring).

6 MTC also urges us to adopt the di strict court’s distinction between “searching for contraband” a nd “being searched for contra band.” App. vol. 5, 1157. But we find this distinction immaterial. Both “searching for” and “being searched for” contraband involve keeping contraba nd out of the prison and maintaining a secure prison environment. Id. Moreover, if MTC means to suggest that the officers are not performing work simply because they are passively undergoing screening rather than actively performi ng some duty, we reject th at suggestion as well. The Court could have relied on such a distinction in Busk , but it did not—likely because such a distinction simply is not relevantto the integral-and- indispensable issue. Indeed, exertion typically is not part of the compen sability analysis. See Alvarez , 546 U.S. at 25.14 Here, if MTC were to forego officer scr eening, officers coul d inadvertently or intentionally bring weapons or other contra band into the prison. The introduction of weapons or other contraband into the prison would most certainly result in a less secure prison. But more importantly, it wo uld “impair[]” the of ficers’ ability to provide security and s earch for contraband, id. at 35, as well as their ability to do so “safely and effectively,” id. at 37–38 (Sotomayor, J., concurring); see also Steiner v. Mitchell , 350 U.S. 247, 249–53, 25 5–56 (1956) (holding that time spent changing clothes and showering was compensable b ecause without doing so, battery-plant workers could not safely perform principal activity of producing batteries in highly toxic environment); Mitchell v. King Packing Co. , 350 U.S. 260, 262–63 (1956) (holding that time spent sh arpening knives was compensa ble because butchers could

not effectively cut meat without sharpe ning). Stated more plai nly, an officer cannot safely and effectively maintain “custody an d discipline of inmates” and “provid[e] security” while also bringing weapons or contraband into the prison. App. vol. 3, 446; see also Busk , 574 U.S. at 37–38 (S otomayor, J., concurring). The security screening in this case is th erefore indispensable to the o fficers’ principal activities. Additionally, preventing weapons orother contraband from entering the prison, by way of the security screening, is “an intrinsic elem ent of” the officers’ security work. Busk , 574 U.S. at 33. Again, the secu rity screening and the officers’ work share the same goal: maintaining a secure prison environment by preventing contraband from inadvertently or intenti onally entering the prison. Thus, under these factual circumstances, we conclude that th e screening is an inte gral part of what15 MTC employed the officers to do. See id. And because the screen ing is both integral and indispensable to the officers’ principal ac tivities, the district court erred in ruling otherwise and in granting summary judgmen t to the officers on this issue. Because the time th e officers devote to undergoing the security screening is integral and indispensable to their principal activities, that activity begins their workday. See id. at 33 (defining principal activities to include those ac tivities that are integral and indispensable to principal activities); Alvarez , 546 U.S. at 28 (noting that workday begins with commencement of principal activities). And under the continuous-workday rule, “[o]nce the work[] day starts, all activity is ordinarily compensable until the work[]day ends.” Castaneda v. JBS USA, LLC , 819 F.3d 1237, 1243 (10th Cir. 2016); see also 29 C.F.R. § 790.6(a) (provi ding that Portal-to-Portal Act does not apply to activities perform ed “after the employee commences to perform the first principal act ivity on a particular workday and before [the employee] ceases the performance of the la st principal activity on a pa rticular workday”). Thus, we further hold that the time the officers devote to recei ving the preshift briefing, picking up keys and equipment, walki ng to post, and con ducting the preshift passdown briefing is also co mpensable under the FLSA. B. Postshift Activities Because the continuous-wor kday rule makes compensa ble all activities that occur from the moment that “the work[]day starts . . . until the work[]day ends,” Castaneda , 819 F.3d at 1243, we begin our postshift analysis with the last activity of16 the officers’ day: returning ke ys and equipment. If that ac tivity is compen sable, then so is the walk from post and th e postshift passdown briefing. See id. Not every officer returns ke ys and equipment, but ma ny do. The district court found that “the number of officers who pick up equipm ent at central control [and therefore must return it] vari es from less than 50% . . . to less than 83 %.” App. vol. 5, 1162. The keys are stored in a fingerprint -activated box, and MTC maintains a key log indicating who possesses each key and when the keys are checked in and out. Access to the equipment is similarly cont rolled; officers use “individualized metal coins, called ‘chits’” to r ecord who checks particular pi eces of equipment in and out. App. vol. 3, 957. Importantly, these proces ses help ensure that inmates do not obtain possession of keys or equipment and thus ar e necessary to mainta in the security of the prison. The district court found that the keys a nd equipment were “to be sure, useful and helpful to the officers in doing their jobs .” App. vol. 5, 1168. In particular, the district court specifically not ed that the officers “use keys to guard the inmates and to lock and unlock doors to ensu re security”; “use radios to communicate with officers at their posts and to give them directions and instructions th roughout the day”; and use “[h]and restraints and pepper spray . . . as both a deterrent and if necessary, to control unruly inmates.” Id. at 1164. Based on these finding s, we have little difficulty concluding that picking up and returning th e keys and equipment is indispensable to the officers’ ability to perfo rm their work. If MTC were to eliminate the keys and equipment (or the corresponding inventory-c ontrol systems), the officers’ ability to17 maintain custody and discipline of inmates and provide se curity in the prison would be “impair[ed].” Busk , 574 U.S. at 35; see also id. at 37–38 (Sotomayor, J., concurring). Indeed, an o fficer “cannot dispense” with the keys and equipment “if [the officer] is to perform his [or her] pr incipal activities” of maintaining custody and discipline of inmates a nd providing security. Id. at 37. Despite this indispensability, the districtcourt concluded that picking up and returning keys and equipment was not “an ‘intrinsic element’ of the officers’ principal activities.” App. vol. 5, 1168 (quoting Busk , 574 U.S. at 35). The district court began its analysis by distinguishing or rejecting each of the cases that the officers cited in support of finding compen sability. In so doing, it emphasized that “the type of tools and equi pment carried by the officers are small in size and not burdensome to carry.” Id. Then, without additional an alysis, the district court concluded that although “certain pre[]shift activities are necessary for employees to engage in their principal ac tivities,” that fact “does notmean that those preshift activities are ‘integral and indispensa ble’ to a ‘principal activity.’” Id. (quoting Alvarez , 546 U.S. at 40). On appeal, the officers argue that checking keys and equipment in and out is integral and indispensable to their principal activities. In support, they first cite a variety of cases in which courts have held that picking up equipment is a compensable activity. See Von Friewalde v. Boeing Aerospace Operations, Inc. , 339 F. App’x 448, 454–55 (5th Cir. 2009) (unpublished); Whelan Sec. , 7 Cl. Ct. at 498– 99; Baylor v. United States , 198 Ct. Cl. 331, 357–58 (1972); U.S. Dep’t of Justice v.18 Am. Fed’n of Gov’t Emps. Local 919 , 59 F.L.R.A. 593, 597–98 (2004). But each of these cases was decided before the BuskCourt refined the integral-and-indispensable test by rejecting formulations of this test that turn solely on whether “an employer required a particular activity” or “whether the activity is for the benefit of the employer.” 574 U.S. at 36. And each of thes e cases turn specifically on one or both rejected rationales. See Von Friewalde , 339 F. App’x at 454–55 (finding that “checking specialized tools in and out of th e tool crib” was comp ensable activity for airplane mechanics because itwas for employer’s benefit); Whelan Sec. , 7 Cl. Ct. at 498–99 (finding time that security guards spent picking up weapons was compensable because it was for employer’s benefit); Baylor , 198 Ct. Cl. at 357–58 (same); Am. Fed’n of Gov’t Emps. , 59 F.L.R.A. at 597–98 (fi nding that time federal correctional officers spent picking up keys and equipment was compensable because employer required such activities). Thus, we do not rely on these cases because their reasoning does not survive Busk

. See Bridges , 875 F.3d at 227–28; supra , note 3. But the officers’ argument extends be yond these supersed ed cases. The officers contend that “when an employee must pick up specialized equipment from his [or her] employer to perform his [or her] du ties, that [activity] is part of his [or her] principal work activity.” Aplt. Br. 34 (e mphasis added). In support, they rely on Brantley v. Ferrell Electric, Inc. , 112 F. Supp. 3d 1348 (S.D. Ga. 2015), and Alvarado v. Skelton , No. 3:16-3030, 2017 WL 28803 96 (M.D. Tenn. July 6, 2017) (unpublished). In Brantley , the district court held th at “collecting and loading the specific parts necessary to co mplete” electrical work was “intrinsic in installing,19 servicing, and repairing electrical equi pment.” 112 F. Supp. 3d at 1371. And in Alvarado , the district court found that time spent picking up and loading required landscaping tools and equipment onto work tr ucks triggered the st art of the workday for landscaping employees. See 2017 WL 2880396, at *5. Here, as in Brantley and Alvarado , the close connection between (1) the keys and equipment and (2) the nature of the offi cers’ work convinces us that checking out and returning these items is “an intrinsic el ement” of providing s ecurity in the prison. Busk , 574 U.S. at 37 ; see also Peterson v. Nelnet Diversified Sols., LLC , 400 F. Supp. 3d 1122, 1135 (D. Colo.) (“Court[s] have lo ng held that pre[]shift preparation of tools or equipment is considered integral and indispensable to th e principal activities when the use of such tools in a readied or activat ed state is an inte gral part of the performance of the employee’ s principal activities.”), appeal docketed , No. 19-1348 (10th Cir. Sept. 17, 2019). In particular, we note that th e specialized nature of the keys and equipment ties the ac t of picking them up and returning them more closely to the officers’ productive work. See D A & S Oil Well Servicing, Inc. v. Mitchell , 262 F.2d 552, 554–55 (10th Cir. 1958) (“[E]mploy ees who transport equipment without which well servicing could not be done[] are perfo rming an activity which is so closely related to the work which they and the other employees perform[] that it must be considered an integr al and indispensable part of their principal activities.”); cf. Smith v. Aztec Well Servicing, Inc. , 462 F.3d 1274, 1289 (10t h Cir. 2006) (finding that activity of putting personal, nonsp ecialized equipment into van was not compensable activity).20 Moreover, the specialized na ture of the keys and equi pment in this case is further reinforced by the ma ndatory procedures that each officer must comply with when obtaining or returning ke ys and equipment. Recall thatin the interest of overall prison safety, the keys are st ored in a fingerprint-activat ed box, and MTC maintains a log of when each key is checked out, who checks it out, and when it is returned. Further, in order to check in or out partic ular pieces of equipm ent, officers must use individualized metal coins— or “chits”—that record w ho possesses the equipment. App. vol. 5, 957. Not only does this invent ory-control system emphasi ze the specialized nature of keys and equipment in the prison context, it further buttresses our conclusion that the process of checking the keys and equipmen t in and out is intrinsic to the officers’ principal activities of main taining custody and disciplin e of inmates and providing security. Similar to the secur ity screening, the inventory c ontrols exist to ensure the overall safety of the prison environment. Indeed, “inmat es are never allowed access to keys for security reas ons,” and the equipment-mon itoring system exists “to monitor the equipment and make sure it does not get into the hands of inmates.” App. vol. 5, 956–57. So the keys and equipment are not just necessary to the officers’ work—the time devoted to checking those ite ms in and out of the inventory-control systems is also closely aligned with their principal activities of maintaining custody and discipline of inmate s and providing security. Cf. Peterson , 400 F. Supp. 3d at 1130 (noting that “activities which are ne cessary to perform one’s work but not21 substantively connected to the actual perf ormance of such work are not considered compensable”). Not to be deterred, MTC argues that we should find this activity not compensable based on the distinction the district court drew between the easy-tocarry keys and equipment at issue here and the heavy and burdensome equipment at issue in cases like Brantley and D A & S Oil Well Servicing . But exertion is not typically considered as part of the compensability analysis. See Alvarez , 546 U.S. at 25 (noting that “‘exertion’ [i]s not in fa ct necessary for an activity to constitute ‘work’ under the FLSA” (quoting Armour & Co. v. Wantock , 323 U.S. 126, 132 (1944))). Nevertheless, MTC ar gues “the case[]law suggests that the simpler, faster, and easier it is to get and ca rry the items, the mo re likely these actions are to be preliminary” and not compensable. See, e.g. , D A & S , 262 F.2d at 555 n.5 (citing with approval regulation that distingui shed between carrying power saw versus carrying “ordinary hand tools”); Clay v. Huntingt on Ingalls, Inc. , No. 09-7625, 2011 WL 13205917, at *10 (E.D. La. Sept. 29, 201 1) (unpublished) (“[T ]he act of merely retrieving and toting a pair of pliers and a sc rewdriver is not going to trigger the start of the continuous workday.”). But MTC’s argument overlooks the distin ct circumstances of this case: although the keys and equipment may be easy to carry, they are not simple or easy to obtain; officers must collect the keys fro m a fingerprint-protect ed box, check the equipment out using chits, and maintain responsibility for those items until they are checked back in at the end of the shift. And perhaps more importantly, this easy-22 versus-burdensome distincti on is not particularly helpful in determining the connection between the tools and the workthe officers are employed to perform. See Busk , 574 U.S. at 36 (noting that integr al-and-indispensable question turns on whether activity “i s tied to” work employee performs); D A & S Oil Servicing , 262 F.2d at 555 (noting that transporting tool s was integral and i ndispensable because tools were “closely related” to work performed). We thus decline MTC’s implicit invita tion to stray from the Supreme Court’s direction in Busk. That direction requires us to de termine whether an activity is integral and indispensable by considering how closely th e activity “is tied to the [employee’s] productive work.” 574 U.S. at 36. Generic tools and equipment like screwdrivers and paperwork are common to a variety of jobs a nd therefore play no specialized role in most types of work, no matter how necessary they might be to a particular job. But items like handcuffs , pepper spray, and prison-door keys are closely connected to the work of providing prison security. Indeed, the district court sp ecifically noted that some of the officers’ “essential functions” were to “[t]rans fer and transport detainees” ; “[r]estrain and secure assaultive detainees”; and “p erform use of force proce dures, including the use of chemical agents to control detainees.” App. vol. 5, 1168. It seems obvious that an officer could not effectively complete thes e “essential functions ” if the officer had not checked out the keys needed to move a detainee, the handcuffs needed to restrain or secure a detainee, or the pepperspray used to control a detainee. Id. ; see also King Packing Co. , 350 U.S. at 262 (holding that ti me butchers spent sharpening knives23 was compensable because dull knives woul d “slow down production,” affect meat quality, and lead to “accidents”). Further, the inventory-control system from which the officers obtain the keys and equipment is essential to the officers’ principal activities of providing prison security because it prevents inmates’ access to the keys and equipment. As such, because of the sp ecialized nature of the keys and equipment, the inventory-control systems, and the offi cers’ principal activ ities in the prison environment, we hold that checking keys and equipment in and out of the prison’s inventory-control systems is integral and indispensable to the officers’ principal activities of maintaining cust ody and discipline of the inma tes and providing security. See Busk , 574 U.S. at 37. And becau se returning the keys a nd equipment is the last principal activity in the offi cers’ workday, the postshift activities th at take place before that—the postshift passdown brie fing and walking back from post—are also compensable. See Castaneda , 819 F.3d at 1243. Thus, the district court erred in granting summary judgment to MTC on this issue. II. De Minimis Doctrine We next consider whether the amount of time that th e officers devote to these compensable pre- and postshift activit ies is de minimis and therefore not compensable. But before undertaking this analysis, we pause to note that MTC’s briefing on the de minimis issue assume s that only the pass down briefings are compensable. As such, MTC never makes the argument necessarily presented by our conclusion that all the pre- and postshift activities are compensable: that the de24 minimis doctrine applies even in these circ umstances. Accordingl y, because MTC did not address this argument in its prinicpal br ief, we could decline to consider the de minimis doctrine at all. See Bronson v. Swensen , 500 F.3d 1099, 1104 (10th Cir. 2007). Yet assuming MTC did make such an ar gument, we reject it on the merits for the reasons explained below. See Kellar v. Summit Seating Inc. , 664 F.3d 169, 176 (7th Cir. 2011) (noting that employer bears the burden of establis hing that de minimis doctrine applies). The de minimis doctrine provides that “i nsubstantial or insignificant periods of time beyond the scheduled working hours, wh ich cannot as a pract ical administrative matter be precisely recorded for payroll purposes, may be disregarded.” § 785.47. At the same time, “[a]n employer may not arbitr arily fail to count as hours worked any part, however small, of the employee’s fixe d or regular working time or practically ascertainable period of time [the employee] is regularly required to spend on duties assigned to [the employee].” Id. The de minimis doctrine applies to “the amount of daily time spent on the additional work.” Reich v. Monfort , 144 F.3d 1329, 1333 (10th Cir. 1998) (em phasis added) (quoting Lindow v. United States , 738 F.2d 1057, 1062 (9th Cir. 1984)); see also Hootselle v. Mo. Dep’t of Corrs. , No. WD 82229, 2019 WL 4935933, at *4 & n.6 (Mo. Ct. App. Oct. 8, 2019) (aggregating, for purposes of de minimis analysis, time de voted to compensable pre- and postshift activities). We apply a three-f actor test to determine whet her work time is de minimis and therefore not compensable: “(1) the practical administrative difficulty of recording the additional time; (2) the size of the claim in the aggregate; and25 (3) whether the [employees] performe d the work on a regular basis.” Castaneda , 819 F.3d at 1243 (quoting Monfort , 144 F.3d at 1333–34). Before applying the three factors, we mu st first estimate the amount of time at issue. Monfort , 144 F.3d at 1333 n.1. “There is no pr ecise amount of time that may be denied compensation as de minimis.” Id. at 1333. And we have approvingly cited cases finding that “as little as ten minutes of working time goes beyond the level of de minimis.” Id. (quoting Reich v. IBP, Inc. , 38 F.3d 1123, 1126 ( 10th Cir. 1994)). Here, the amount of time that officer s spend daily on compensable pre-and post-shift activities is not en tirely clear. The district court concluded that the amount of time was “substantially less than . . . eight minutes pe r shift.” App. vol. 5, 1181. The district court appears to have deri ved that number from the parties’ summaryjudgment briefing: MTC calculated eight mi nutes per shift as the most favorable number for the officers, and the officers likewise estimate d eight minutes per shift (although they elsewhere argued that the amountof time was more than ten minutes). Because the district court conclude d that only the passdown briefing was compensable, it accordingly found that the time was “ substantially less than . . . eight minutes per shift.” Id. (emphasis added). But because we have concluded that all of the officers’ pre- and postshift activities ar e compensable, we assume that the amount of time is at least eight minutes per shift. 7

7 Indeed, it is likely more than eight minutes per sh ift. As MTC acknowledges, its ten-minute adjustment rule is based on the approximate amount of time it takes to get from the time clock—imme diately following the security screening—to the posts. And because those ten minutes occur at both ends of an o fficer’s shift, the amount of26 The first de minimis factor, “the pr actical administrative difficulty of recording the additional time,” weighs in the officers’ favor—the time clock already tracks most of th e time at issue. 8 Monfort , 144 F.3d at 1334 (quoting Reich v. N.Y.C. Transit Auth. , 45 F.3d 646, 652 (2d Cir. 1995)). Th e time clock is located just past the metal detector and captures all of the compensable activities except the screening itself. Further, it is possi ble to estimate the average time the officers devote to screening. See Kellar , 664 F.3d at 176–77 (noting thatbecause employees performed the same activities every day, “it would have been possible to compute how much time” employee spent on them); Rutti v. Lojack Corp., Inc. , 596 F.3d 1046, 1059 (9th Cir. 2010) (noting that even though “it may be difficult to determine the actual time” at issue, “it may be possible to reasonably determine or estimate the average time”). Thus, because MTC already re cords the majority of the time at issue and could reasonably estimate the time that it does not record, this factor weighs in the officers’ favor. Next, “the aggregate amount of compen sable time”—a factorthat considers both the aggregate claim for e ach individual officer as well as the aggregate claim for all the officers combined—also we ighs in the officers’ favor. Monfort , 144 F.3d at

time could be as much as 20 minutes. (It is likely not mo re than 20 minutes because if an officer works more than ten additiona l minutes on either end of a shift, MTC pays him or her for that time under the ten-minute adju stment rule.) 8 The district court found ot herwise, but that is becau se it considered only the passdown briefing. We reac h a different conclusion on this factor because we consider all of the officer s’ compensable activities, beginning with the security screening and ending with the retu rn of keys and equipment.27 1334. The district court di d not make an express findi ng about the aggregate amount of compensable time; instead, it concl uded that the aggregat e claim for all the officers combined was substan tially less than the amount that MTC provided in its summary-judgment motion, $355,478, b ecause that number included compensation for time devoted to no ncompensable activities. 9 The district court then weighed that finding in MTC’s favor because a number le ss than $355,478 was substantially less than the $1.6 million that we wei ghed in the plaintiffs’ favor in Monfort

. But we cannot rely upon the district court’s less-than-$355,478 conclusion
because that conclusion tu rned on the underlying determination that only the passdown briefing was compensa ble. Because we have c oncluded that all of the officers’ pre- and postshift activities are compen sable, we assume that the aggregate claim is at least $355,478. 10 And more importantly, the dist rict court erred in treating Monfort as if it set a baseline below which all claims are negligible; rather, th e court there merely noted

9 MTC calculated this amount based on an officer who worked eight additional overtime minutes per shift, fi ve days a week, for three y ears, and then multiplied that figure by 122 plaintiffs. 10Indeed, as with the amount of time at issue, the aggreg ate claim could be higher. On appeal, the office rs provide a higher per-office r claim estimate “[b]ased on a representative sample of 15% of the officers” over “the four-year time period covered by this suit.” Aplt. Br . 56. According to the office rs, each officer ’s back-pay claim for this four-year time period aver ages $7,093.28. Although the officers do not provide an estimated aggreg ate amount in their briefing, multiplying their per-officer estimate by 122 plaintiffs results in an estimated total aggregate claim of $865,380.16. We need not accept this estimate to complete our analysis here. But we acknowledge it in order to emphasize both that(1) we base our de minimis analysis on assumptions and estimates, rather th an definitive numbers, and (2) those assumptions and estimates are arguably conservative.28 that a $1.6 million clai m “was very large.” Monfort , 144 F.3d at 1334. In fact, more moderately sized claims are not automatically negligible. See Perez v. Mountaire Farms, Inc. , 650 F.3d 350, 374 (4th Cir. 2011) ( noting that in case involving 280 employees, individual claims for $425 per year or $2,550 over six years were “significant”); Lindow , 738 F.2d at 1063 (suggesting $1 per week for 50 weeks would not be de minimis claim). Indeed , MTC cites no cases in which a court weighed a claim of this size in the employer’s favor. T hus, we conclude that the aggregate size of the officer s’ claims is substantial a nd weighs in their favor. As to the third factor, we conclude th at the regularity with which the officers perform this work also favors the officers. See Monfort , 144 F.3d at 1334. The district court found that this factor balanced equally between the parties because (1) “[i]t is apparent that a ll officers receive pass[]down br iefing[s],” but (2) “there is no fixed time any of them mustshow up on post for thes e briefings.” App. vol. 5, 1182. We, of course, look at more than just the passdown briefings. And it seems clear that most officers pe rform most of thes e activities during mostshifts. Indeed, MTC requires both the security screening a nd the passdown briefi ngs, and it designed the ten-minute adjustment rule to account for the time it ta kes to get from the security screening to post. See Monfort , 144 F.3d at 1334 (weighing regularity factor in employees’ favor where activities took about ten minutes each day); Jimenez v. Bd. of Cty. Comm’rs of Hidalgo Cty. , 697 F. App’x 597, 599 (10t h Cir. 2017) (unpublished) (rejecting de minimis doctrine for required five-minute briefing period because time was regular and ascertainable). As such, we weigh this fact or in the officers’ favor.29 In sum, and contrary to the district c ourt’s conclusions, al l three factors weigh in favor of the officers: MTC already records most of the time at i ssue, the aggregate claim is substantial, and the officers regularly engage in these activities. As such, we find that the time at issue is not de minimis and conclude that the district court erred in granting summary judgmentto MTC on this basis. See Monfort , 144 F.3d at 1334 (finding that time was not de minimis base d on size of claim and regularity of work and despite administrative diff iculty of recording time). III. Suffer or Permit to Work Next, MTC argues that even if the officers’ activ ities are compensable, the officers should not be allowe d to claim compensation for them because MTC did not know that the officers were doing this wo rk. The district court did not reach this argument because it ruled against the officers on co mpensability. But we have reached the opposite conclusion. Thus, we address—but ultimately reject—MTC’s position that it need not compensate the officers because it did not know the officers were engaging in this work. The FLSA requires employers to pay employees when the employers “suffer or permit [employees] to work.” 29 U.S.C. § 203(g); see also Mencia v. Allred , 808 F.3d 463, 470 (10th Cir. 2015). This provision crea tes a kind of FLSA estoppel doctrine: if an employer does not know that an employee is doing certain work, then the employer is not required to pay the employee for that work. See Mencia , 808 F.3d at 470. But if the employer is aware of the wo rk and therefore “suffer[s] or permit[s]” the work, it must pay the employee. § 203(g); see also Mencia , 808 F.3d at 470.30 Stated differently, “[a]n empl oyer who is armed with [knowledge that an employee is working overtime] cannot stand idly by a nd allow an employee to perform overtime work without proper compensation, even if the employee does not make a claim for the overtime compensation.” Fairchild v. All Am . Check Cashing, Inc. , 815 F.3d 959, 964 (5th Cir. 2016) (second alte ration in original) (quoting Harvill v. Westward Commc’ns, L.L.C. , 433 F.3d 428, 441 (5th Cir. 2005)). Here, MTC argues that it did not know th e officers were working outside of their scheduled shifts because the office rs (1) did not complete time-adjustment forms to request overtime pay and (2) si gned an acknowledgeme nt form included with each paycheck stating th at they submitted such a form for any overtime work conducted before or after thei r shift. In other words, MT C maintains that it does not owe the officers compensation because it did not know they were working before and after their shift times. But as the officers point out, the facts here do not permit a logical leap from the absence of time-adjustment forms to MTC’s lack of knowledge. Indeed, the cases that MT C cites to support its pos ition—that an employee’s failure to use an overtime-compensation syst em always means that the employer does not know about the work being done —involve an employer’s constructive knowledge. See White v. Baptist Me m’l Health Care Corp. , 699 F.3d 869, 873–77 (6th Cir. 2012) (discussing whether em ployer should have known employee was working during lunch break); Hertz v. Woodbury Cty , 566 F.3d 775, 781–82 (8th Cir. 2009) (discussing appropriateness of jury instruction about whether employer should have known, based on nonpayroll records, that employees we re working during31 commutes and m eal breaks); Newton v. City of Henderson , 47 F.3d 746, 748–50 (5th Cir. 1995) (discussing whether employer should have known employee was working overtime despite employer’s express denial of overtime authorization and employee’s failure to report overtime). These cases are notrelevant here becaus e, as the officers point out, this case involves MTC’s actual knowledge that the of ficers are engaging in these activities. In particular, MTC requires both the security screening and the passdown briefing. It cannot simultaneously require an activity and claim to be unaware that employees are engaging in that activity. Further, it is undisputed that MTC often has supervisors c onduct the preshift briefing; knows the officers check out keys and equipment becau se the officers use the i nventory-control procedures; and knows they walk to and from their posts because they show up for work. In sum, MTC pays the officers for the eight hours they are at their posts. But it knows that the officers are working outside those eight hours, on their way to and from post. And MTC “cannot stand idly by and allow [the officers] to perform overtime work without proper compensation, even if” the officers did not claim overtime compensation using the time-a djustment forms or sign acknowledgment forms. Fairchild , 815 F.3d at 964 (quoting Harvill , 433 F.3d at 441). We therefore reject MTC’s contention that it did not “suffer or permit ” the officers’ work on their way to and from their posts. § 203(g). IV. Rounding Finally, we consider the officers’ rounding claim, in which they allege that MTC’s ten-minute adjustment rule routinel y rounds down their work time, resulting32 in systematic underpayment. Rounding is the practice of “recording the employees’ starting time and stopping time to the near est [five] minutes, or to the nearest onetenth or quarter of an hour,” or to some other consistent time increment. § 785.48(b); see also McDonald v. Kellogg Co. , No. 2011 WL 6180499, at *12–13 (D. Kan. Dec. 13, 2011) (unpublished) (considering roun ding claim based on te n-minute adjustment rule); Russell v. Ill. Bell Tel. Co. , 721 F. Supp. 2d 804, 819 –20 (N.D. Ill. 2010) (considering rounding claim based on eight-minute adjustment rule). Federal regulation permits roun ding as long as “it will not re sult, over a period of time, in failure to compensate the employees prope rly for all the time they have actually worked.” Id. ; see also Corbin v. Time WarnerEntm’t-Advance/Newhouse P’ship , 821 F.3d 1069, 1075 (9th Cir. 2016) (noting that federal regulation has endorsed use of rounding for over 50 years). Stated differe ntly, a valid rounding policy must be “neutral, both facially and as applied.” Corbin , 821 F.3d at 1076 (quoting See’s Candy Shops, Inc. v. Superior Court , 148 Cal. Rptr. 3d 690, 701 (Cal. Ct. App. 2012)). It must allow for rounding both up and down, so that an employee is sometimes compensated for time not spent working, and sometimes not compensated for time spent working. See id. at 1077. Recall that under MTC’s ten-minute-adjustmentrule, if an offi cer clocks in or out more than ten minutes before or afte r his or her shift time, MTC will pay the officer based on the time cloc k rather than on his or her scheduled shift. But if an officer clocks in or out fewer than ten minut es before or after his or her start time, MTC will pay the officer based on his or he r scheduled eight-hour shift rather than33 the clock time—in other words, MTC rounds th is time off. This rule is facially neutral because it r ounds both up and down. See id. That is, an offi cer assigned to a 6 a.m. shift who clocks in at 5:51 a.m. and cl ocks out at 2:09 p.m. will be paid for eight hours, even though he or she worked at le ast an 18 additional minutes (nine on either side). Similarly, an officer who clocks in at 6:09 a.m. a nd out at 1:51 p.m. will also be paid for eight hours, even though he or she worked 18 fewer minutes (nine on either side). But the officers presented evidence sugge sting that the ten-minute adjustment rule is not neutrally applie d. In particular, they subm itted a represen tative sample showing that about 94% of the time, the of ficers were clocked in —and therefore were performing compensable pre- and postshift activities—for longer than their eighthour shift time. And a rounding policy that works in the employer’s favor 94% of the time is probably not neutrally applied. Yet the district court reje cted the officers’ rounding claim. The basis for its decision is not entirely clear, but it concluded that because the officers are paid for their scheduled shifts unde r the ten-minute adjustmentrule, their “theory of ‘rounding’ . . . violations is incongruous with” their other claims. App. vol. 5, 1155. In other words, the district court appear s to have decided th at because this case involves claims for overtime compensation—that is, for work completed outside of34 the eight-hour shift—MTC’s ten-minute ad justment rule “does not constitute ‘rounding’ as that concept is us ed in wage[-]and[-]hour law.” 11 Id. We disagree that rounding can never be relevant when cons idering claims for overtime compensation. The district cour t cited no authority to support this proposition, and we have fou nd at least some authority to the contrary. Specifically,
in Russell , the district court denied summary judgment to the employer defendant on the employees’ rounding claim because if the employer’s “time [-]rounding and log[-]out policies often cau sed [employees] to work unpaid overtime in increments of under eight minutes, then th ese company-wide practices may have resulted in unpaid overtime work .” 721 F. Supp. 2d at 820 (emphases added). Indeed, the district cour t’s conclusion that roundi ng is never relevant to overtime claims appears to bypass the ulti mate issue in this case. We are not concerned here with whether MTC pays the officers for their full eight-hour shifts; instead, we are concerned with whether MT C compensates them for work completed outside of those eight-hour shifts. And if the ten-minute adjustme nt rule routinely rounds off that compensable overtime, as the officers’ evidence suggests, then the officers’ rounding theo ry remains viable.

11 The district court’s ruling may also have turned at least in part on its conclusion that the officers ’ activities after clocking in but before arriving at their posts were not compensable: the district court noted that “ under a true rounding system, employees are working immediatel y upon clocking in.” App. vol. 5, 1154. Yet because we conclude here that thes e activities are compensable, the district court’s rounding ruling is flawed to the ex tent that it turned on its compensability ruling.35 At this stage of the litigation, MTC ha s not countered the officers’ evidence on the non-neutrality of its ten-minute adju stment rule. Indeed, MTC’s only argument against the rounding claim, both below an d on appeal, is that the ten-minute adjustment rule does not amount to roundi ng because the officers are not doing compensable work during the ti me that is rounded off the time clock. We have found to the contrary. Thus, although “employees who voluntarily come in before their regular starting time or remain after their closing time[] do not have to be paid for such periods” as long as “the y do not engage in any work,” those are not the facts of this case. § 785.48(a). And because it appear s that the officers ha ve met their initial burden to show that they are routinely paid only for their shift ti me even though they regularly arrive early, leave late, and do workduring that time, the district court erred in granting summary judgment to MT C on the officers’ rounding claim. Conclusion For these detention officers, undergoing the security screening and checking specialized keys and equipment in and out of a centralized inventory-control system are integral and indispensabl e parts of the principal activ ities that they are employed to perform: maintaining custo dy of inmates, searching fo r contraband, and providing security. As such, those two activities are compensabl e under the FLSA, and they begin and end the officers’ workday. Accord ingly, the pre- and postshift activities that occur in between—the preshift briefing, walking to and from post, and the passdown briefings—are part of the officers’ continuous workday and are therefore compensable.36 The officers devote at least eight minutes per shift to conduc ting these pre- and postshift activities—more th an a de minimis amount of time under all the relevant factors. Further, at least two of these activities, the secur ity screening and the passdown briefings, are require d by MTC policy, so MTC know s that the officers are engaging in this work. Additionally, becau se MTC’s compensation system appears to routinely round down the time that the of ficers are working, th e officers’ rounding claim survives summary judgment. Accordingl y, we reverse the district court’s order awarding summary judgment to MTC a nd remand for further proceedings.