@DavidZH said in Pin change interrupt not firing with MySensors: It did! Thanks a bunch! I had a feeling it was to be found in that part of the code. Great! Strange thing is: it still returns -1 as wake up reason. And that brings me back to my original problem. Well, that function is setup to either return the interrupt number, or -1 if it didn't wake from interrupt. You woke it differently, hence the return code of -1, see here. When I want to add a timed sensor by setting a time as last argument, the node will not wake up when an interrupt takes place. It does register the interrupt, as the counter increases with every press. But it will only wake when the timer expires and only then display the updated counter. The actual sleep method differs whether a timeout is passed or not, see here. I would have to consult the datasheet and dive into the different sleeping methods, but that probably is the reason of not waking up. Again, you are using the library in an undocumented/untested way, so, unless you're able to read/modify the code yourself, I advise you to stick to the suggested use cases.