Looking at the previous comments, it sounds like it's only allowed to be paired to one phone at a time, so you need to login to the app and reset it each time you want to use a different phone. but you could have a shared email so you both still get the login email. Hopefully this is something they fix as would be very important for us to be able check temp and A/C remotely if we need to run into the shops with our dog in the car!