Which of the following are types of magnetic contact sensors used in security installations?

• A. Garage Door
• B. Surface and recessed
• C. Surface, Recessed and Garage Door
• D. Magnetic contact sensors are not used

Answer: (C)

Magnetic contact sensors come in several mounting styles to fit different door setups. Surface-mounted sensors attach to the outside of the door or frame and are easy to install, making them a common choice for quick security upgrades. Recessed sensors are installed inside a mortised area in the door frame or edge of the door, giving a cleaner look and better tamper resistance. Garage-door sensors are designed specifically for the unique needs of garage doors, often with mounting and spacing suited to the larger, moving door.

Because all three forms—surface-mounted, recessed, and garage-door sensors—are used in security installations, the option that includes all of them is the best choice. The other options omit one or more valid types, or wrongly suggest such sensors aren’t used.