Teardown: 433MHz window sensor

We’ve had a look at at 433Mhz window sensor before, but are they all the same? Let’s check another one:

osm900-1

Ist this one different? It definitely is a bit larger. Why?

osm900-3

It runs on AAA batteries. That makes replacing the batteries easier and most likely cheaper than the special 12V battery we saw in the other sensor. If you want to use it as a security device, it is also nice to see that there is a switch connected to the case. If somebody tries to open the device, it will also send a message.

osm900-2

On the back there aren’t any surprises. Just the transmitter chip with a few external components and an LED.

The protocol used for the 433MHz RF transmissions is trivial. There is no encryption. This means it is extremely simple to record the signal from the sensor and play it back again. It depends on your use case, if this is a problem.

As the module tested before, this one also only sends a signal when the window opens, not when it closes. Therefore it can’t be used to detect if a window is open or close.

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