Wireless sensors that require no external power source or battery maintenance? If this can be perfected, hopefully the next thing that can be tackled is the common household smoke detector! Seriously, this is an important advance in sensor technology and will enable many things that we cannot even think of right now.
How much of a temperature differential is required between the "warm surface" and the room for the system to work? How does the device efficiently shed heat so that it doesn't rise to the substrate temperature and lose the ability to generate power?