Earl
We had one installed when we moved into the house. Our DD was paranoid about living out "in the real world", after being in base housing her entire life.
Our house is huge [it's a Victorian built in 1865] and it is nice that when you are on the third floor [not that I get up there much anymore!!] you can hear the "beep" and know someone has come into the house.
Now that DD is older, she cannot 'sneak' in at 3am without us hearing the beep!! Payback is a b*#@h!!