Here’s how cheap contact sensors gave my smart home superpowers

Contact sensors, often called door or window sensors, use magnets to detect open or closed states. You can use this information and changing these states to do all kinds of cool things in your smart home.

Suspend heating or cooling when windows are open

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I’m happy to manage my home’s heating and cooling manually, rather than leaving it on all the time at a set temperature. But if I lived in an apartment or newer house, I’d probably just buy a fancy thermostat and let it do its thing, in which case this tip would come in handy.

One thing you probably want to avoid is wasting money heating or cooling a space when the windows are open. If you tend to leave the central air conditioning on all the time at a set temperature, contact sensors are highly compatible with your management style.

Forget turning off the heat or air conditioning every time you need fresh air; use the “open” state of a contact sensor to automatically pause your system. Using the status of your contact sensors as a condition, you can have the system automatically engage every time you close the house.

Receive reminders about open doors and windows

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I had a bike stolen from my garage a few weeks ago because I forgot to close the garage door at night. Since then, I have designed an automation that checks the status of the garage door at a defined time and sends me a critical alert if it is open.

Another way to do this (which several commenters have pointed out) is to create an alert that sends a notification if the door is left open for a set amount of time, such as 10 minutes. Use the “open” state change to trigger the countdown, then condition the alert on the door being still open.

This could work for just about any door you don’t want to leave open for an extended period of time, whether it’s a screen, baby gate, or back door – perfect if you have pets or small children you don’t want outside.

Receive tracking notifications to empty the washing machine

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Receiving an alert on your smartphone that the washing machine has finished its cycle is one of the best ways to use an energy monitoring smart plug. But if you’re like me, getting just one alert on your iPhone isn’t enough. I have proven many times that I am capable of ignoring a notification.

With a contact sensor stuck on the washing machine door, you can create an alert that continually reminds you to empty the machine until the sensor goes off. Best of all, you can create the entire automation using one powerful plan that only requires changing a few settings and checking a few boxes.

Trigger lights when motion sensors won’t cut it

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The motion sensors work well, but they’re not perfect. They’re big, they require a clear line of sight, and they eat away at batteries. Although infrared is a good choice for triggering an event, these sensors are much less effective at detecting an ongoing presence, because if you stand still for too long (or walk out of range), they will register that no one is there.

Contact sensors might be a better choice in many cases. For example, if you have a kitchen cabinet or pantry that you want to light based on when a door is opened, these are perfect. You don’t need to stand within range to keep the light on; you can simply use the “open” state to turn a light on indefinitely and the “closed” state to turn it off again.

Design intrusion alerts and makeshift alarms

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I once built a makeshift alarm system using Home Assistant and cheap IKEA contact sensors, perfectly suited to my house. When the alarm system is activated, an alert sounds and lights turn on if a particular door or window is opened after I go to bed or when I am away from home.

Doing this is pretty simple, going as far as creating a simple trigger to turn the “alarm” on or off from Apple’s Home app and automatically turning the alarm on at night and turning it off again in the morning. Such a system can be as complex or as simple as you want, because Home Assistant offers many options.

A silent system could be used to send you an alert whenever a sensor is triggered and you’re not home (there are presence detection indicators you can use, like the Home Assistant companion app for iPhone and Android). You can then check all the cameras to see what’s happening and decide if you need to take further action.

You can do the same for dog doors and cat flaps, or if you live in a shared apartment, receive an alert every time someone enters your private space.

Record access to doors or drawers

In my home, Apple Home and Home Assistant keep sensor logs so you can see exactly when they were triggered. You can even determine how long these sensors have been “open” by checking the time between the two readings.

This gives you an access log to all the areas you want to monitor. It could be the cupboard you keep the cookie jar in, it could be the porch screen door to see if the delivery guy really knocked on the door, it could be your backyard gate to see if someone walked the dog today (but make sure you have a weather-proof contact sensor for the latter).

I opted for cheap IKEA Parasoll sensors for my Home Assistant setup, which are being phased out in favor of Matter over Thread Myggbett sensors. Brands like Aqara, TP-Link and Sonoff also offer this type of solution.