The lights are on, but nobody's home.
My outdoor lights are on a timer - and Intermatic Model SS7 Series - which you might want to avoid. In fact they no longer seem to sell the model I have even though Home Depot had plenty at the store today.
It is a programmable timer that replaces a standard light switch allows you to set multiple on/off cycles. This morning I noticed that at 9 am, well past the normal off setting, my front lights were still on. I pushed the switch and nothing happened. I looked at the display on the switch and it was displaying "no Op".
I grabbed the instructions and checked the troubleshooting section, only to find that "no Op" means that the "mechanism is inoperative". Their suggestion? Replace the timer.
I've had the device for about a year and a half so it is no longer under warranty. I bought this timer expecting a quality product. Instead I seem to have purchased a disposable piece of junk.

