Dying of curiosity here, so......I'm askin'.
Sounds like a real "guy thing".
Would you believe?
Aw Hell.
Once upon a time, in a land called Downtown, the Police Department bought 100+ new Unitrol 800s for the fleet, and learned fairly quick that the switch in the 800 SUCKETHED.
They tried to pawn off replacing switches onto the City Radio shop and found the units back at the police garage, with a complementary jar of Vaseline and strong suggestion where the Unitrols should be installed.
Word quickly reached the Jr genius of a local Ambulance/hearse/fire extinguisher/dry ice/ice business that a need existed for siren repair, so naturally, he saw $$$$$$$ to put in his pocket. He already had a TV repair guy working part time, and worked a deal with him to play with his magic soldering iron, between calls. The TV guy figured sitting at a bench playing with his soldering iron beat hell out of bagging ice, so an electronic siren shop came to be.
Junior learned he could buy switches from Unitrol, and speaker voice coils from Atlas in quantity and they arrived to sit under lock and key in the office, because Junior trusted nobody. A maximum of 2 switches and 2 coils were allowed to be in the siren shop, in another locked cabinet.
All was peace, love and joy UNTIL Mr TV relocated 2 speakers above the ceiling of the shop because everything else he tried including a box of insulation blew his ear drums out. That stunt damn near caused Mr TV to cease breathing when he blasted 2 crews out of the bunk room 20 feet away, because he failed to understand the space above the ceiling was the plenum for the air conditioning.
The oft referenced Plan Q was called for, and Mr TV learned the term Dummy load. Carbon resisters such as were often used for that purpose cost money, and given the presumed peak output power of a siren, a large pile of resisters would be needed. Plan Q.2 was called up. What's in stock in the barn that should have the ability to absorb power in the Audio range and dissipate that power without making noise.
Light bulbs of course.
It didn't take long to understand 4 120 volt 100 watt lightbulbs wired together in parallel became 4 flashbulbs when Yelp was hit. Mayhaps 12 volt bulbs would do better. Grab a headlight, it sucks a lot of watts and it looks sturdy. Again, Flashbulb with cracked glass. Maybe multiple bulbs. Well at least the glass didn't crack. Put the bulbs back in the boxes, glue the box back shut and stick them back in inventory, and nobody tell the mechanic.
Further experimentation continued. Plan Q.22 involved using a speaker driver screwed into a piece of pipe sticking in a bucket of water. It killed 90% of the sound, but also required mopping the floor. Elementary Physics tells us energy can neither be created or destroyed, and that bucket of water proved it.
Naturally, when word starts getting around the barn what a siren will do to a light bulb, the well known "Yer $#!^^!ng me" effect comes into play, and many people need to see it for themselves. It didn't take long for multiple different sirens to be "tested" to prove what they'd do. The problem became finding a lightbulb in the barn that wasn't already blown up.
When the mechanic dragged a laundry cart full of blown "new" headlights into Junior's office and announced every damn one was junk, Junior got on the phone with the supplier and demanded free replacements. The salesman who brought them was smart enough to know new headlights don't leave the factory sealed with chewing gum, and refused.
So
The moral of this story is if you're going to play with your siren, pretty much regardless of manufacture, go to an electronics surplus dealer who still has inventory of the ancient ceramic resistors the size of a stair railing, and buy 9 100 watt 1 ohm resistors and wire them in series. Then spread the resistors out in a thick walled drywall mud bucket and fill the bucket with transformer oil to dissipate the heat. That will survive siren testing for durations of 10 seconds without problem as long as you let the bucket cool between tests.
It's kind of a rework of the beloved Heathkit Cantenna sold by the thousands to Ham Radio operators back in the 70s.
Moral #2, if you absolutely insist on metering the voltage to a siren speaker, put your meter on the highest range and cross your fingers.
PS: if you need used Unitrol 800 units, I can stuff some in a USPS 1 rate box and ship them to you real cheap at least till snow flys here.