Some sirens require three-phase AC for the motors. I went through a bunch of Federal and a few other manufacture tornado sirens in the Midwest at one point in my career. Some of them looked like vacuum cleaners or spinning tubas and most of them were installed at the height of the Cold War. One had so much torque that it split the pole over the years. I thought it might go spinning off the pole one day and into the firehouse next to it.
I had these removed and replaced with Whelen WPS electronic sirens which were basically big vehicle sirens that ran stacked 400 W drivers for each speaker segment. The motorized AC sirens were almost bulletproof (literally... some of them had bullet holes), but the electronic ones were high maintenance. Getting AC hooked up without a meter was a nightmare, so I went solar. The batteries were on a 3 year replacement cycle (I had to stretch them to 4 years because of budget), the drivers would open (seemed to run in batches), or the amps would short and fail. Over the years they got more reliable, especially after AC power was eliminated. Solar didn't cook off the batteries and the only lightning threat we had now was a direct hit, not a power line spike. We used radio controlled activation and the link radios (first batch were OEM'd by EFJ, subsequent batches were Ritron) were two-way devices. The siren was controlled by a microprocessor device. Very finicky on audio characteristics, but resistant to spoofing. After we got the process down, we were installing about 5 per year at a cost of about $20k for the equipment and $5k for the installation labor (union men) and pole.
In that configuration, the sirens were as reliable and independent as an alerting receiver, unless they got hit by lightning or a truck.
BTW, you CAN do siren control through a trunked system, and even a P25 system! Before I vested out, I asked for $2M (~150 tornado sirens, equipment, and technician time to retrofit each device) to remove the analog VHF radios, replace them with 700 MHz radios, pull the controller, and equip them with ACE3600 RTUs that would also control the sirens and provide diagnostic feedback. Ultimately, they decided to keep the VHF system intact just for that (and they STILL needed to buy and install narrowband radios). Oh well.