Something for water running would be nice.
It'd also be nice to have something more generic that plugged in between appliances and the wall outlet that measured the current drawn. When something is on/running it draws more current. You could then have receivers with lights to indicate when something is on/running and turn off when the current drops back down. It also be nice if it flashed when there was a state change to draw attention to the receiver. Receivers should accept signals from multiple sensors and the sensor should be programmable to recognize which currents to trigger on/running and off/not running. The receivers and sensor could also use the electrical wiring for basic network connectivity instead of radio or RF, although optional ability to interface with text messaging (if it can interface with home network) or portable unit would be nice for outdoors. Sensors that screw into light sockets would also be useful for knowing that a motion sensor light was tripped outside.
The Chinese have made a device that plugs into taps and lights up the water if it's on. Good for people with bad eyesight too. Also doesn't need batteries because it's powered by the running water.
Unfortunately it suffers from bad QC, so it's pretty iffy. If someone in a country that cares more about QC could make one, that'd be good