Alarm systems are ok but to be honest, a dog is the biggest deterrent as the burglars won't take a risk with the dog being either noisy or aggressive.
If you want an alarm, it's worth spending the money for a properly installed one as they're much less prone to false activations. You can also omit rooms that have pets in when set.
A cheaper option though is to fit dummy bell boxes with battery powered leds in so it looks to the opportunist thief like you have an alarm.
