Power supply via UPS, leakage sensor, other UART devices

[gasinskiy]

1. Can I supply voltage to the KC868-A8S module from an uninterruptible power supply, which produces 13.8 V when powered from the mains. And what is the lower voltage threshold at which the board will stop working?

2. Can I connect any other UART device instead of the telephone module? For example PZEM-004T?

3. Can I connect the Neptune SV005 leak sensor this way? It has 12 V, in the case of a UPS 13.8 V voltage between ground and output, when triggered 0V. 

Thank you!