heated O2 sensor circuit question

[Ed]

I plan on relocating my O2 sensor further down into the header since the
original spot reads off only 2 of the 4 cylinders. Thing is, the
original sensor is a single wire, and I think I'd need a heated one for
the new location. 
Any idea how to wire the heater circuit? Is it safe to wire the circuit
to a switched (engine on) power source or was the heaer designed to shut
off once it reaches operating temp?

-Ed