Security System FAQ
Q: What is the difference between NO (normally open) and NC (normally closed) alarm contacts, and why do I care?
A: Normally closed contacts complete a circuit when they are in their "normal" state -- i.e. when a door or window being monitored is closed. When the protected door or window opens, the circuit is broken, triggering an alarm. Normally open contacts complete the circuit when the door or window being protected is opened. Normally closed contacts are more prevalent in DIY and household installations, probably because they have a built-in failsafe; if the circuit is cut, a normally closed alarm zone will sound an alarm.
Q: What's better - A wireless or hardwired security system?
A: With the techonology available today, good wireless systems can be nearly as reliable as hardwired. The main factor in determining whether to go wireless or hardwired is usually the ease of installation. In a house under construction, it is fairly easy (and inexpensive) to run hardwired contacts to each entry point. In an existing home it becomes much more difficult due to fishing wires, damaging drywall, etc. Another option is a hybrid system, which allows hardwired and wireless zones, giving you maximum flexibility if you want to expand the system. See the Security Systems Overview for more information.