By popular demand, here's a follow-up on my post from four months ago about home security gadgets. In that post I mentioned two devices that I subsequently purchased and used.
First was the Keep-I volumetric air pressure alarm.
Keep-I monitors air pressure. If any change occurs, such as a criminal opening a door or window, the alarm sounds. When the device is set to fine recognition mode, a simple touch on your door handle will trigger the 95 decibal alarm. Within the space protected by the Keep-I, you can move about freely, your kids can play and your pets can run around. This alarm allows you to live your life while still protecting yourself and those you love, giving this high tech system great practical advantages over infra-red and motion detecting alternatives.
It sounds like a neat idea, and the science actually works very well. The problem is that opening and closing interior doors can set the alarm off by changing the air pressure gradients in the house, so you either have to leave them all open or disable the alarm before opening one. This limitation, though completely understandable and unfixable, makes the Keep-I awkward to use at night, particularly if you ever have to go to the bathroom. I expect it would work very conveniently in a hotel room or other smaller enclosed area with fewer swinging interior doors.
The second system I bought was a big box of magnetic door and window alarms. Each unit has two parts, one that attaches to the door or window and the other that attaches to the frame. When activated, the unit makes a loud noise if the door or window is opened. They're very simple and cheap -- about $2 each if you shop around.
One disadvantage is that the door frames in my house are poorly angled and not well-suited for these devices. The two parts of each unit need to be mounted within a centimeter of each other, and the way my frames are shaped makes this difficult to do without having the device obstruct the path of the door. Still, I managed to rig up all the doors on my house and I set the alarms every night. The devices mount perfectly on my window frames.
A second disadvantage is that the double-sided tape that comes with the devices can come undone in high temperatures. Units placed in sunlight may ocassionally fall off and start screeching until their batteries die if no one is home to shut them off.
All in all, both devices have their uses and can increase home safety for a very modest price.