Smart home hack: Use an old hard drive magnet as a slim alarm sensor

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Disclaimer: This worked with our alarm sensor, but there's no guarantee that it will work
with your sensor.  Make sure that you test this out to ensure that there are no false or
missed alarms.

So we just got a new door at our house and we wanted to find a less obtrusive way to get our alarm sensor on the door.

Entry Sensors

Most entry sensors have two pieces, the bigger part with a sensor, battery, and wireless communication back to the base station and a second smaller piece that contains a magnet that will trigger to indicate when the door sensor is near (closed) or away (open).

This new door sits in a slightly recessed door frame and we didn’t want to have a big magnet stick out on the new door frame so we tried the following hack to avoid the second piece. The end result was to get something like this:


Using an old hard drive magnet

If you’re like me, you probably have a bunch of old 3.5 and 2.5” hard drives sitting unused. A few months ago I took several of these apart in order to securely dispose of the data spindles. Hard drives tend to have some really strong and small magnets in them. These are about as thick as a penny and 0.5” to 1” in length, making them the perfect size to fit between a door and a door jam.

Removing the magnet

The biggest challenge you may have is prying them off of the metal chassis that they are sitting in. Normally it’s attached to a piece that looks like this:

We found that the best method was to try to slide them a bit so that one edge of the magnet is hanging off an edge of the chassis, then pry them off. Once you get them out they should look like a small piece of metal as thick as a coin and that is slightly bent like the one below. Note: this one is attached to a piece of Command strip tape:

Installation in the door

This part is rather simple. Just cut a Command strip tape to the perfect size, attach it the magnet and then attach this to inside of your door jam


You might want to test with temporary scotch or blue tape to make sure the sensor position works for you and that your door closes fine without hitting the magnet. Then once ready peel the back off the Command strip tape and attach.

That’s it.

And now with the other sensor on the door:

For many sensors, you can really use a variety of magnets as long as it has the right polarity and strength. You can also even try taking apart the actual magnet sensor and just using the magnet on it’s own, if they fit your specific needs. The alarm sensors are meant to work when “near” a magnet and it’s important that you test the exact positioning. We found that if the sensor is too close or too far from the magnet then it did not work reliably. It’s critical that you test this out and ensure that the magnet and placement is compatible with your sensor.

If you are looking for a great do-it-yourself alarm system, please check out SimpliSafe Wireless Home Security System w/ optional 24/7 Professional Monitoring

Best of luck with the hack…



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