I helped my cousin last week install a alarm on his garage as its best part of 300 metres from the main house but it has 240v, he opted to simply buy a 12v transformer as found in use for cb radios etc and a quality pager car alarm using extra functions on remote apart from usual arm/disarm to open close garage door and has 2 sirens, one being a air raid style one on the roof and by heck when its tripped we can hear it from the main house with windows closed and his phone is text to alert him of garage has a issue, just a idea as it works very well for him