Best security alarm for the house?
A dog with a loud and fierce bark.
Train it not to touch food until it is told to. That way when the scum bags drop the poisened meat (yes these toe-rags do that) through the letter box the dog won't touch it.
We've had a couple of prowlers round the back but they decided the better of it when our mutt kicked off.
Previous mutt has saved two of my bikes in the past. Had to be parked outside in the front yard. Dog in the front room, 3AM bike tea-leafs sneak in, dog kicks off tries to jump through front room window, bellowing it's head off.
Would be thieving scumbags were so far up the street by time I got down stairs they were almost out of sight. And I was down there in treble quick time too.
Next best thing make friends with OAP's across the road, best street security system devised, any strange persons moping around the place or checking out the house and they're straight on the phone. Right on.

And good for taking parcels in when they get delivered and you're not home.
Word soon gets round the criminal fraternity which bits of town to avoid.
Ains.