Short answer: a door/window contact consists of two parts: a sensor on the fixed frame and a small magnet on the door or window. As long as they're touching, the contact is closed. If the door or window opens, the magnet moves away and the sensor immediately reports this to the alarm control panel — before anyone is even inside.
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How a door/window contact works
Inside the sensor is a switch that responds to the magnetic field of the separate small magnet. When the magnet is right against it, the switch is at rest. If the magnet moves away because the door or window opens, the state changes and the sensor sends a wireless signal to the control panel. If the alarm is armed, the siren goes off and you get a notification on your phone.
That makes a door/window contact your first line of defence. Burglars often get in by forcing a door or window, or by stepping in where something has been left open. In both cases something opens — and that's exactly what a door/window contact reports.
Which doors and windows first?
Start with the entrances a burglar can reach most easily:
- the front door, back door and the door to the garage or utility room;
- the sliding patio door or French doors to the garden;
- ground-floor windows, especially at the back and out of sight of the street;
- first-floor windows that can be reached via an extension, shed or wheelie bin;
- basement windows and roof hatches.
Fitting in 5 steps
1. Clean and degrease the spot, so the sticker adheres well.
2. Stick the sensor on the fixed frame, on the side where the door or window opens.
3. Stick the magnet on the moving part, so that when closed it sits right next to the sensor.
4. Keep the gap small. The LockSense Pro works up to approx. 2 cm between sensor and magnet, even at an angle.
5. Test it. Open the door or window and check whether the notification arrives in the app.
No screws needed: all LockSense models are fitted with the included sticker, without tools. That's handy in a rented home, and you can move a sensor if the spot turns out not to be right after all.
Which LockSense should you choose?
| Model | Connection | Battery and extras |
|---|---|---|
| LockSense | Wireless via 433 MHz | Energy-efficient, fitted with a sticker |
| LockSense Pro | Wireless via 433 MHz | Battery up to 4 years, works up to approx. 2 cm apart and at an angle |
| LockSense Elite | 433 MHz and LoRa, up to 500 metres | Battery up to 10 years, warns when the battery is low |
For an ordinary home, the LockSense or LockSense Pro is enough. The Elite is intended for situations where the distance to the control panel is large: a shed at the bottom of the garden, a warehouse or business premises with lots of walls in between.
What a door/window contact doesn't detect
A door/window contact only responds when the door or window opens. If someone smashes the glass and climbs through the hole, the magnet doesn't move. For large glazed areas, a sliding patio door or windows that can't be opened, a glass break detector such as the ShockSense is a good addition: it responds to shocks and vibrations at windows and doors. Read more in What is a glass break detector and do you need one?. And a motion detector in the room behind picks up anything that still gets in.
So how does a door/window contact work?
A door/window contact consists of a sensor on the frame and a magnet on the door or window; when it opens, the contact is broken and the sensor immediately reports this to the alarm control panel.
Our solution
Alarm system for your home
Wireless sensors you install yourself, alerts straight to your phone and no ongoing monthly fee.
View the options
Frequently asked questions
Which side do you stick the door/window contact on?
The sensor on the fixed frame, the magnet on the part that opens, both on the side where the door or window opens.
How far can the magnet be from the sensor?
As close as possible. The LockSense Pro works up to approx. 2 centimetres between sensor and magnet, even at an angle. Always test after fitting whether the notification arrives.
Does a door/window contact work on a sliding patio door?
Yes. Stick the sensor on the fixed part of the frame and the magnet on the sliding part, so that they sit right next to each other when closed.
Do I need to drill holes for a door/window contact?
No. You stick the LockSense models onto the frame with the included sticker, without screws or tools.
How long does the battery of a door/window contact last?
That varies by model. The LockSense Pro lasts up to 4 years, the LockSense Elite up to 10 years and warns you itself when the battery is low.
Sources and references
- Politiekeurmerk Veilig Wonen (Dutch police quality mark), Burglary methods (in Dutch) — consulted September 2026
- Politie (Dutch police), Tips to prevent home burglary (in Dutch) — consulted September 2026
- Neroo.nl, Product data LockSense, LockSense Pro, LockSense Elite and ShockSense
