Start with the layout
Choosing sensors goes better when you start with a floor plan than with a product list. Sketch the building, mark every exterior door, ground-floor and reachable window, sliding door, garage door and basement entrance, then note the rooms an intruder would probably cross. The sensors you pick should answer two questions: where could someone get in, and where could they be noticed once inside?
Door and window sensors
Contact sensors are the workhorse of most systems. They have two parts: a magnet and a switch. When the door or window opens and the parts separate, the sensor signals the panel. They are simple, reasonably inexpensive and tend to produce few false alarms when fitted properly. Because they detect opening rather than movement in a room, they can trigger the moment someone enters.
Points to weigh:
- Fit and gap. Aligned parts matter. A loose or misaligned magnet can cause trouble reports or false alarms. Check the manufacturer’s allowed gap.
- Surface or recessed. Surface-mounted units are easy to install and replace. Recessed units are less visible but are more work, especially in finished frames.
- Specialty types. Sliding windows, garage doors, rolling shutters and steel doors may need a different style, such as heavy-duty or overhead-door contacts.
- Wired or wireless. Wired contacts use no batteries of their own, while wireless ones are flexible but need battery care. Our comparison of wired and wireless options covers that choice.
Not every window needs a sensor. Windows that are small, high up or permanently fixed might not be worth it. Prioritize the ones a person could realistically use, as discussed in the page on securing windows and sliding doors.
Glass-break detectors
Glass-break detectors listen for the sound patterns of breaking glass, and some also sense the shock. One detector can cover several windows in a room if they are within its stated range and line of sight. They fit rooms with many panes, large glass doors or storefront windows where fitting contacts on each pane would be impractical.
The main considerations:
- Check the detector’s rated range and what glass types it handles, since laminated or coated glass may behave differently from ordinary glass.
- Heavy curtains, furniture and distance can reduce performance.
- Placing it near sources of sudden noise, such as kitchens, can bring false alarms.
- A glass-break detector does not notice an intruder who opens a window instead of breaking it, so it is typically a supplement to contacts rather than a replacement. Our comparison of glass break and contact approaches explains the difference.
Motion detectors
Interior motion detectors watch a space and trigger when they sense movement. They are useful for covering rooms a burglar would have to cross and for areas without convenient doors or windows. Placement and type matter, and homes with animals need models designed to tolerate pets; read more about pet immunity before assuming a sensor will ignore your dog or cat. Airflow, heating vents and sunlight can sometimes cause unwanted triggers, so aim them away from such sources. Read our page on motion detectors for the finer points.
Other sensors
Depending on the site, you may add:
- Vibration or shock sensors on safes, glass or fences.
- Smoke, heat and carbon monoxide devices, which follow local codes and must be properly located. Get advice from the local authority or a licensed professional.
- Water leak and freeze sensors for basements, utility rooms and empty buildings.
These protect against hazards other than intruders and are often worth considering regardless of the burglary risk.
False alarms
False alarms annoy neighbors, waste time and, in many places, can bring fees or fines. Most come from user error and from poorly chosen or poorly placed devices, not from faulty equipment. To reduce them:
- Choose sensors designed for the environment, including pets, humidity and temperature.
- Mount devices according to instructions and test them before relying on them.
- Leave time for entry and exit.
- Train every user in the basics.
- Replace batteries before they run out.
Our article on reducing false alarms at home and work goes deeper.
Battery considerations
Wireless sensors run on batteries. Life varies with device type, activity level and temperature, so go by the manufacturer’s estimates and the system’s low-battery messages rather than a fixed idea. Keep a record of when batteries were last changed, buy the correct type, and test after replacing. The system should warn of low batteries and report sensors that stop communicating; if the panel you are considering does not, treat that as a drawback.
Putting it together
A typical layered approach might look like this: contacts on all realistic entry points, a glass-break detector where there is a lot of glass, a motion detector covering the main route through the home or shop, and life-safety sensors as required. Add more only where the layout calls for it. Whatever you choose, test regularly. A sensor cannot guarantee protection, but an appropriate, maintained set can improve the odds that a problem is noticed early.