I had an idea of an iPhone app but I'm not sure if the methods are entirely legal. For that reason I thought I would come here to ask.
Where I live, in Canada, it can get pretty cold. Hence, I had the idea of making the iPhone heat up slightly (to a safe level) so the user could heat up their hands and to prevent the phone from shutting down to the cold temperatures (a common problem in the winter).
To do this I had the idea of running a cryptocurrency miner on the device. For those who don't know, cryptocurrency mining can be a CPU-intensive process and can cause it to heat up, but the process can also generate cryptocurrency that can be exchanged for other currencies (CAD, USD).
Would it be illegal to use this method to heat up the phone if the user is not told how the phone is heated up as it generates an income that they would not receive?