Been around quite a while. https://www.ant-supplies.uk/airsoft-external-parts/blank-cartridge-tripwire-alarms.html
Fitted probably the least expensive thing to the Multi's new exact starter wiring but rather satisfying too. Mod list is getting smaller.
Been there and done that. Thankfully (for me) they aren’t loud enough to do serious hearing damage but proper shit you up at the time. I could see curtains twitching on the neighbours house which was good. I still use them on the shed but use a baby monitor in the garage, anyone so much as farts in there and I will hear it. Best security you can get for £20.
After having my sheds done over just before Christmas and a huge amount of stuff getting pinched (including a 5" gauge steam engine) when I move into that house the sheds will have tripwires like Vietnam.