We did a class exercise in my lighting for camera class where we had a person rotate lights with gels on them on two arms clamped onto a c-stand, which bounced off a mirror.

I could be remembering the exact specs wrong but is this the only way to do it?

Lee,
you described lights in the post but the title of the thread is sirens so if you want a siren wait by the firehouse til they make a run then capture it, watch for clipping. If you want lights the way you did it works or rent a couple of strobes, 1 red, 1 blue, turn 'em on and adjust to taste. They should be on a tilt swivel so you can aim them up or down, if not mount to a small board and tilt that to get the desired effect.
Since my oldest son is a 13 year veteran of the fire department when I did training vis for them they obliged my every whim and fantasy with lights and sirens but alsa, that was a few years ago and appearently that footage has gone to raw footage heaven.

ah thanks yeah i meant police siren lights

Moderator note: title changed from "sirens" to "lights."

1. Buy this:
https://www.speedtechlights.com/product_detail.php?catid=5&id=126
2. Wire it up to a car battery.
3. Use it.
4. Sell it after the production

Any computer geek can tell you that sometimes, emulation is more trouble and expense than just using the real thing.

Or there's this:

Spinning Beacon Party Light- Party City (http://www.partycity.com/product/spinning+beacon+party+light.do?sortby=ourPicks&size=all&from=Search&navSet=disco+light)

In San Francisco there's this magical place called The Prop Co-op. In this magical place you can rent one. Perhaps there might be one near your shoot?