We consider similar opinions during product development and as a result we implement couple of solutions:
In case you lost your phone or wall mounted tablet die, there is still physical switch on Smart Road device to switch ON and OFF all connected devices
System can be installed in that wat you still have manual switch which takes priority
In case of total power supply lost our system remember which devies had which state and will recreate the state
Even we assume very unlikely situation - that our device will become totaly unresponsive. You can still easily unplug it from your system with one screw driver and continue your journey.