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2 motion detectors and a 3 way switch.

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New Member
I currently have a 3 way switch set up. One switch at the top and one at the bottom of my basement stairs. I want to add two motion detectors in my basement. I keep forgetting the lights and want it turned off after XX time no motion is detected from either of them. I found these site....http://launified.org/installing-a-motion-sensor-to-an-existing-light-fixture/ ....and.... http://www.renovation-headquarters.com/wiring-multiple-motion-sensors.html don't know how to incorporate the two switches (3 way) that are already here. Thank you for any help. Note, I don't want the switches to determine weather the the motion sensors are powered or not, so if I turn the lights off, I would like the motion sensors to be able to turn the lights on if that's possible. If that's not possible, I definitely need the motion sensors to at least be able to turn the lights off regardless of which switch is turned on/off. Hope that's not confusing, thanks.
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Well-Known Member
Unsure if two sensors can be paralleled, something near your wishes, with only one sensor that should 'see' the entire stairwell :


If two sensors can be paralleled, the second sensor could be anywhere in the basement... I think.
The '|' mark next to 'sensor' is a typing goof. Ignore.
'lamp' could be 'lamps'


New Member
Thanks for that. Yes the sensors can run parallel as in the link in the OP. So I understand what I'm looking at. The power hits the motion detector first, then the switches, then the lights. When the sensors see me the lights turn on, and I can switch them off if I want, or wait until no motion is detected.

However, based on the drawing,
1/ If I switch the lights off manually, the sensors wont turn them back on until I flip the switch again? So basically, when I go to turn the switch off I have to flip the switch twice to put everything back in position for the motion detector to turn the lights on automatically?
2/ If the sensor is off, can I turn the lights on?
3/ If the sensor is off, do I have to flip the switch twice to turn it on?


Active Member
Firstly, it is two-way switching
And secondly you cannot turn on the light if you have the sensor in charge of the light too.
You have to turn ON the sensors and then the sensor will automatically turn on the light for a short period of time and then keep it on while the PIR is detecting motion.


Well-Known Member

1/ Switching lights off manually, the motion sensor(s) will not turn them on.
But if the lights switches are left in 'on' state, the presence/motion of a hand towards flipping switches should enable them.

2/ No. But again, if the switches are left in 'on' position, the sensor will see the hand motion towards the switch and no need to flip..

3/ If the sensor is the one that turned off lights because saw no motion recently, it will turn the lights on by just approaching the hand towards any switch if in range.

All depends much on actual location/position/layout of your everything. Think of the sensors as 'enablers' of the switches in my sketch. No motion anywhere, all goes off regardless of switches status. Motion will restore last switches status. If left manually off, stay off. If left manually on, will turn on.

If there is a sensor in the basement and another in parallel by the stairwell (doubled at top of sketch), any or both enable the switches status as left the last use.

I think...

Edited - Added : I believe as Colin says above, title of the thread should be more like
"Two motion detectors and two 2-way switches"
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Well-Known Member
Most Helpful Member
What I did in that situation was to add an LED indicator to show when the current taken by the light was flowing through the motion detector’s contacts. When the switches are on, the LED goes out so I can see if the switches have been left on.
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