With mine, you can make it stay on all the time by shutting off power momentarily, then back on. (Fortunately, it has a switch.)
To make it go back to "sensing" mode, you power it off for 30 seconds or so, then back on. You might have to shut off the breaker for that circuit if you don't have a switch.
You probably had a momentary power outage that set it "on", and now you can't get it to go off.
[This message has been edited by rpxlpx (edited October 11, 2002).]