Peter Burgess said:
I know of one remote accommodation site (remaining anonymous for obvious reasons) that have plans to install mains electricity at great expense because amongst other reasons they feel its the only way to take necessary security measures. All previous measures such as steel shutters and smashproof windows not being considered sufficient in this day and age. In the case of your site it's probably a case of raise the money to do this yourselves or lose the kit.
Have you considered a stake out? It worked wonders some years ago when cavers' stuff was being pinched regularly in Wales. Repeated incidents might just be one or two people causing a disproportionate amount of chaos.
Never really rated electronic alarm systems - they seem to go off so often nobody really takes a lot of notice of them.
Taking the UBSS hut as an example, I would consider a bird scaring gas gun
http://www.molevalleyfarmers.com/pd4_VERMIN_BIRD-SCARE_25320_BIRD-SCARER-SCATTERBIRD-MARK-3.htm
Presuming the hut has gas, and there must surely be enough electronics boffins within the club to adapt and develop an initiation/firing/override system, this would be a cheap alternative. They're fearsome things, especially to the unaware and unknowing. It would also have the advantage of raising awareness amongst the local residents that something was going on.