This sort of thing usually happens if your devices are paired with something else. In some cases this means FulGaz can’t see them at all, in others, they don’t transmit any data. To fix the problem, try the following
- Quit FulGaz
- Turn on any other apps that have ever connected to your sensor
- In those app, disconnect or forget your sensor
- Start FulGaz again
If it's still not working, on an iPhone or iPad, quit and restart bluetooth. If you're using an Apple TV, turn it off and on again.