The floodlights are on while the sun is out! This is an almost-certain sign that the motion sensor has failed and needs replacing. Outdoor motion detectors don't last forever. Here's what you need to know to determine that it's time to replace one and to do that safely.

This controller for outdoor floodlights is the most common type available. It combines a motion sensor with a built-in photocell.

Did I just say this thing has two switches in it? Well, yes. It does. Two sensor switches connected in series, at that.

What all that means in plain language is that an outdoor light controller takes the incoming power and sends it to a photocell first. A photocell is a normally-closed switch -- with a light receptor -- that opens, and stops the electricity from going further, if there is enough light entering its receptor. When there isn't enough light, it closes and the power is sent to the next switch. That switch is the motion detector. It's a normally-open switch that closes, letting the power flow through it, when "motion" is detected.

Both of the switches in an outdoor light controller are designed to fail closed, thereby turning the lights on all the time. Why? Well, we install these devices for security, don't we? Given that, most of us prefer to have the lights stay on if there's a problem, rather than have them stay off. That's also why one answer when troubleshooting a security lighting system is, "If the lights are staying on, the problem is almost certainly the motion sensor."

So, now that we know that the problem is the sensor, how do we fix it?