Alarm Sensor Types Overview: Doors, Windows & Motion

A home security system is only as good as its sensors. Panels, apps, and cameras get the marketing attention, but it is the small devices on your doors, windows, and walls that actually decide whether the system sees a problem or ignores it. This overview walks through the main alarm sensor types, what each one does, and where they make the most sense in a normal house. If you need a broader system-level picture, start with Home Security Systems Explained and come back here to plan the details.

1. Door and Window Contacts

Door and window contacts are the backbone of almost every alarm system. They are simple magnetic switches that tell the panel whether something is closed or open.

How They Work

• One piece mounts on the frame, the other on the moving part (door or window).
• When the door or window is closed, the magnet keeps the circuit in its normal state.
• When it opens, the magnet separates and the sensor reports a change.

Contacts are ideal for controlled, obvious entry points. For more on which doors and windows to prioritize, High-Risk Entry Point Analysis explains how to rank them by real-world risk.

Where to Use Contacts

• Main entry doors (front, back, and commonly used side doors).
• Ground-level windows that can be accessed from yards, porches, or roofs.
• Basement doors and walkout entries.
• Garage side doors and service entries.

Contacts give clear “open vs closed” information, which is useful for both alarm events and basic status checks (for example, verifying the garage side door is shut for the night).

2. Motion Detectors

Motion detectors watch spaces instead of specific openings. They are meant to catch someone who is already inside, whether they entered through a monitored door or not.

Passive Infrared (PIR) Motion Sensors

• Detect changes in heat patterns as people move across the room.
• Work best when mounted 6–8 feet high, aimed across paths of travel.
• Less effective when aimed directly at windows, vents, or heat sources.

A few well-placed motions can backstop your contacts. They are especially useful in central hallways, stairways, and large open-concept living areas. For help planning coverage, see Zone-Based Security Planning.

Where to Use Motion Detectors

• Central hallways that most people must cross to move through the home.
• Rooms with multiple entry points where you do not want a contact on every door.
• Areas protecting valuables, such as living rooms with electronics or home offices.
• Near stairways where an intruder would have to pass to reach bedrooms.

Motions are often set to trigger instant alarms when the system is armed “away,” but can be disabled or ignored in “stay” modes so you can move inside without constantly disarming the system.

3. Glassbreak Detectors

Glassbreak sensors are designed to detect the sound or vibration of breaking glass. They fill a gap that normal contacts miss: a window that is smashed instead of opened.

Acoustic Glassbreak Sensors

• Mounted on walls or ceilings within range of multiple windows.
• Listen for the specific frequency pattern of breaking glass.
• Can cover several windows in the same room if placed correctly.

Shock/Vibration Glassbreak Sensors

• Mount directly on the glass or frame.
• Detect vibration from impacts and breaks.
• Better for single high-risk windows or doors with large glass panes.

Glassbreaks are a good fit for rooms with large fixed windows that do not open, or for big patio doors. They are not a replacement for door contacts, but a supplement when you want better coverage of glass-heavy areas.

4. Environmental and Safety Sensors

Many alarm systems can also monitor non-burglary conditions: water leaks, temperature extremes, and other hazards. These do not replace dedicated life-safety devices like smoke alarms, but they can add useful early warnings.

Common Environmental Sensors

• Water leak sensors: Detect water on the floor near heaters, washing machines, or under sinks.
• Temperature sensors: Alert you to freezing conditions that could burst pipes.
• Heat sensors: Sometimes used in garages or dusty areas where standard smoke detectors are not ideal.

These sensors are most effective when combined with basic fire safety measures. For smoke and detector placement, refer to the Smoke Detector Placement Guide.

5. Specialty Sensors (Garage, Gates, and More)

Beyond the standard types, you will see specialty sensors that solve specific problems around the home.

Common Specialty Options

• Tilt sensors: Used on overhead garage doors to detect when the door is open.
• Outdoor motion sensors: Built to handle weather and reduce false alarms compared to indoor motions placed outside.
• Gate or fence sensors: Monitor exterior gates or perimeter access points.

These are worth considering if you store tools, equipment, or other valuables in outbuildings and want the alarm system to cover those spaces as well as the main house.

6. Wired vs Wireless Versions

Almost every sensor type comes in both wired and wireless versions. The sensor’s job stays the same; only the way it talks to the panel changes. Choosing between wired and wireless is less about sensor type and more about how you want the entire system built.

• Wireless sensors are easier to install and move.
• Wired sensors are more permanent and require less long-term maintenance.
• Signal and interference concerns are covered in detail in Wireless vs Wired Security Systems.

In practice, many homes use a mix: wired sensors where cables were easy to run, and wireless add-ons for later upgrades or hard-to-reach spots.

7. Putting It Together in a Real Home

The goal is not to use every sensor type; it is to use the right few in the right places. A typical balanced setup might include:

• Contacts on main doors and key windows.
• One or two motions to watch central movement paths.
• Glassbreak coverage in rooms with large fixed windows or glass doors.
• Leak sensors in areas where water damage would be expensive.

How you monitor those sensors also matters. If you are deciding between self-monitoring and professional monitoring, DIY vs Professional Security Systems explains how response and responsibility differ.

Once you know which sensors you need and where they belong, the rest of the system—hub, app, and monitoring—has something solid to work with. You are no longer guessing; you are intentionally covering real entry points and risks.

Next: Choosing a Security Hub