I'm placing my bets on a CLM or some other British-standard unit made in Canada. Darn, I just looked at the test schedules, what an inconvenient time to venture two hours out of town for. xD
99% sure that's a 20/24. They sound like a normal 10/12 siren, just slightly higher pitched because they spin at 1800RPM instead of around 3300RPM like a normal siren.