For those of you who have a tendency to leave your door/gate open for whatever reason, you can get a time-delayed door alarm such as this wireless one from GE.
Of course, you can always build yourself one with a bit of soldering and parts from your local Radio Shack. You can follow the directions here on how to make your own time-delayed door alarm using a door sensor, 555 timer chips, piezo, and small parts.
And if you want to make more complicated alarms, don’t forget to check my DIY on how to make an alarm system in 3 minutes that I did 3 years ago.
While we are talking about alarm systems, if you are interested in general home alarm systems and spy alarm systems, check out BrickHouseSecurity, they’ve got an array of great home alarm system gadgets you can get.
Also, if you want to get a home alarm system but don’t want to pay for monthly monitoring fees, Intellahome.com sells these DIY home alarm systems that will call your cellphone/phone number when someone breaks into your house. Well, that’s not going to help you catch the crooks but still, better than no alarm system. And SmartHome.com has a similar DIY alarm system kit except you pay $8.95 for monitoring.