hey I recently bought a big loud alarm that runs off 240v. I am looking to purchase a wall mounted keypad with door alarm sensors from ebay. where can i find a relay that can use low current to trigger 240v? I wouldn't ming having a complex setup where i would have to step it up twice to get up to 240v just need parts to get it there. pretty much putting my own LRAD system in my crawlspace to run the my the burgulars off. conventional alarm setup from a local company wont work at this point (cost efficiency+moving soon). I am moving soon and the alarm will be reupfitted for another type of trigger at my next residence. plus who wants monthly fee's? and when the crooks hands are on their ears they will have a tough time grabbing stuff wont they?

I am very familiar with wiring stuff up as I work on late model cars regularly and wire up all my own stuff for my shop (supply from the road to the 240 welder and 240v compressor and everything in between)

 

You can use a triac to drive a relay with a 24VAC coil. The 24VAC is supplied via a step down transformer from the 240VAC (or 120VAC). An example of the relay is G2R-24-AC24. $6.55 from digikey.

 

The keypad should have a "form c" relay on board. You can wire from the 24Vac transformer to the "C" of the keypad's relay, and from the "N.O". of the keypad's relay to your Omron G2R-24-AC24 (or whatever you use). No triac is needed.