The Desert Hawks use a version of these. We use a $2.50 Harbor Freight window alarm. They are taken seriously at local milsim games but no longer usable at big events such as Lion Claws. They are too easily reused.
This what I use as well as other people around
https://www.youtube.com/watch?v=nyNWh-6UDeo$153 for the grenade (ordered directly from SWAT), or $175 will get it and the shotgun primer adapter (again directly form the manufacturer). I paid $150 with the adapter from Spazz here on AA. There are other people in the mix that want to be dealers as well.
I use shotgun primers at $0.04 for each shot, and I have thrown it in a game or demonstrated it no less than 180 times. That is $158 spent. 180 Thunder B's would cost $450 in shells and C02 cartridges, not to mention the cores that usually become unserviceable quickly and need to be heavily modified to get them to go off in a timely manner.