Multi-story houses have a certain flair—reflecting a sense of prestige and class. Many new homes thus have multiple levels, and the upper floors with most of the bedrooms and a bathrooms can see a lot of traffic across the stairs. This can make for a hazardous passage, especially in the dark of night. The top landing of a staircase is often in a dark area anyway, often deprived of a window and depending strictly on a light fixture for illumination. And carrying a tray of dishes, or a hamper of laundry, can make it difficult to flip a simple light switch.
Enter the motion detecting light system. These might seem futuristic or complex, but the truth is, they're easy to install yourself.
What You Need to Start
Most household stairways are equipped with a light fixture that can be turned on or off at either level of the stairway with two 2-way switches. The wiring for these usually involves a three-wire NM cable running from the bottom floor up to the top landing. Then there's typically a 120 volt feed going to either of the 2-way switches, and usually from the top landing switch’s electric box, another cable is fed to the light fixture. From such a setup, it's very easy to replace both switches with a movement sensor at the top landing and a timer at the lower level.
Once you're finished, the movement sensor at the top will get activated and turn on the light fixture when someone moves within its range. It's usually equipped with an adjustable sensor so it will disconnect when adequate sunlight is present.
A timer at the bottom of the stairs, connected in parallel to that sensor, will probably complete the required task of turning on the lights better than another sensor. Since it's located on the main floor where a lot more traffic is generally present, a sensor would likely trigger with unnecessary frequency. That said, you can go either way with this part of the design.
How to Make the Change
Safety Warning: The first thing to do is to go to the main electrical panel and TURN OFF THE BREAKER AFFECTING THAT PARTICULAR CIRCUIT. Never work on live wires! Before opening up the electrical boxes, the absence of power should be confirmed by trying to turn on the light.
With this done, the next objective is to identify the cable bringing in the 120 volts source. Even though you've turned the power off, you need to know that the lightbulb in the fixture in question is working, or you won't get an accurate read of the circuit.
Remove the decorative plates should from both switches—unscrew both switch plates and pull them out from their electrical boxes to reveal their cables.
A multimeter or Ohmmeter with the setting on resistance (Ω) or continuity should be checked for workability by shorting the leads together and confirm the reading at 0 ohms (Ω). If it reads "∞" or "open circuit," you might need to replace the batteries in the meter.
If you find an electrical box containing one three-wire cable and two two-wire cables with black wires connected to the switch, this is the one you should work on first, but only if the other electrical box has one three-wire cable ONLY. If the other box has more than one cable, this is an unusual circuit and you should consult a certified electrician (or post the issue to our DIY forum). That said, this is a very unlikely configuration.
After locating one of the 14/2 cables connected to the circuit, remove the wire connectors from the black wire and the white wire to expose the copper tips. Then remove one black wire from that 14/2 cable and isolate it from the cluster.
Put the leads of the multimeter across the isolated black wire and the white exposed wires to confirm very low resistance if the light bulb is connected to those specific wires. If it is the case, the other 14/2 cable would carry the 120 volts feed.
If on the previous step the meter reads "∞" or "open circuit," this cable is likely the 120 volts feed, in which case the following check should be performed:
Remove the black wire originating from the other two-wire cable and do the same continuity test across its isolated black wire and its white wire, it will confirm the low resistance reading of the light bulb on the meter dial or screen.
The Figure 2 schematic can then be used for re-wiring the circuit.
If both electrical boxes contain one three-wire cable and one two-wire cable with the black wires connected to the switch, the 120 volts feed is in one of the boxes while the light fixture is wired to the other electrical box, and that will probably be at the top landing of the stairs. This is the box to begin with to confirm your findings.
After removing the wire connectors from the black and white wire clusters, exposing their copper tips, separate the black wire from the 14/2 cable from the cluster.
Using the multimeter on the same setting, put the leads can across the isolated black wire and the exposed white wires to confirm very low resistance if the light bulb is connected to those specific wires. If the reading the meter reads "∞" or "open circuit," this cable is likely the 120 volts feed, in which case there's a good possibility that the light fixture is located halfway up the stairway, either on the wall or the ceiling.
Either way, if it worked with two-way switches, it will still work with the sensor and timer. At this point, the two-wire cable in the other box should be tested to confirm a low resistance reading on the multimeter. The wiring to install your new timer and motion detector can then be done following the schematic of Figure 3.
The completed project will look pretty similar to a regular light switch, but now it will be on guard to help you traverse the stairs at any time, from dim days to dark nights!