As previously stated, the Detroit People Mover is operated by the Detroit Transportation Corporation, which as a Michigan Public Body - Corporate entity, can and has set-up it's own certified police force, known as the Transit Police.
7 Detroit Transportation Corporation office photos. A free inside look at Detroit Transportation Corporation offices and culture posted anonymously by employees.
www.glassdoor.co.in
The two analog FM voice repeater sites are atop Book Tower & Westin Book-Cadillac, which is strange because the structures are quite close to each-other, The freqs are licensed for high HAAT & ERP, meaning it's licensed to be a high-profile/wide-coverage system not only covering DTC's People Mover operations, but also Detroit Dept of Transportation buses, stations/stops, etc. It's strange that the 900MHz mobile (/portable) radios are authorized for 100 watts output.
ULS License - Business, 896-901/935-940 MHz, Conventional License - WPXE752 - Detroit Transportation Corporation
I'm over 1750 miles away from Detroit, but I determined the above via just a few minutes on Google...
When I lived right next-door to Joe Louis Arena in downtown Detroit from 1997-2002, I rode the DPM about 40-60 times a month (I had a monthly pass), for work & pleasure, and listened to their Security & Maintenance talk-groups on the old City of Detroit analog 800MHz Trunked system that also had DPD SWAT, Narc's, Mayor's Security, HQ Surveillance Team, etc. & some other secret squirrels in-addition to boring Water & Sewerage Dept Ops & Security, et al. On a daily basis, Transit Police would mostly respond to homeless-types loitering at the stations, and fare-evaders detected by CCTV cameras monitored by their control center, but during major events like the Detroit Auto Show at Cobo Hall, Red Wings games & concerts at Joe Louis Arena, Freedom Festival, etc. they'd have personnel at the DPM stations closest to the major events managing the crowds. DPM train PTC/SCADA was on 900MHz ISM, DSSS but may have moved to something else by now. I expect the real entertainment would be monitoring the Transit Officers assigned to the buses. I once had a friend who was a D-DOT bus driver in the 1980s & 1990s (until he medically retired due to being shot -- Duane, are you out there?) who told me some insane stories about some of the crimes & depravity that'd occur on those buses. And before Transit Police existed, Detroit PD Tactical Services Section would have 'Bluebird' details of plainclothes or U/C officers riding the bus and in the event of a crime aboard, they'd radio on good old 453.875 (old DPD TSS repeater) to the TSS vehicle behind them that they had a situation, and the bus would pull-over so the Bluebird detail uniformed officers could board the bus & take-down the criminal.