In a security system, disrupting the magnetic contact, such as by opening the door or window, will trigger the alarm.
Wired contacts are cheaper, but more difficult to install than wireless contacts, which can easily be moved to another location and reused. Wired contacts can cost anywhere from $3 to $20, and wireless contacts range from $20 to $70.
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.