In the hallway of my house I have a Caseta Wireless On/Off switch (PD-6ANS) and a PICO remote connected together.
I don’t know anything about motion sensors but is there an inexpensive way to put a motion sensor in the hallway to control the switches… I don’t want to replace the switches?
Do these sensors just plug into a receptacle or do you attach to the wall someway?
Do you have a smartthings hub? If so, you will have a lot of options. 
Most motion sensors are battery operated, but there are some which which plug-in. The battery operated ones are quite small and light and can be attached pretty much anywhere with something like a 3M command strip.
If you don’t have a smart things hub, do you have an echo plus or echo show second generation? If so, there are some motion sensors that will work with that set up.
Yes I should have mentioned I have a SmartThings hub.
Can you recommend a motion sensor?
The obvious choice, as it will definitely be fully supported by Samsung, is their own Zigbee based motion sensor. At ~$20, it is pretty affordable as well.
One thing to be aware of, since it sounds like this might be your first Zigbee device, is that you may need to establish a decent Zigbee mesh network with a few AC-powered devices, like the following Samsung Zigbee outlets. (Note: It must be a Zigbee outlet, not a WiFi outlet.) Strategically placing these around your home will establish a solid Zigbee mesh network. This allows the battery powered devices, like the motion sensors and door/window contact sensors to connect through one of these Zigbee repeater devices back to the Hub. Feel free to try without the outlets, especially if your ST hub is relatively close to where you plan to deploy the motion sensors.
Thanks for the replies! I like the $20 price of the sensor but really didn’t want to have to buy another device to flesh out the mesh network… guess I can try without first.
I already have a Z-Wave network isn’t there a sensor just as good for that or are there other differences?
You have a lutron bridge too I assume?
I have a Lutron motion sensor in my basement and it fine for the basement control. On or Off. However, with a sensor like what ogiewon mentions and the use of a smartthings hub with WebCore (SmartApp), you can get some seriously cool lighting control.
My whole house is Caseta ( i was maxed out at 50 devices but they just raised it to 75!). Most of my main rooms have motion sensors so…
I created a virtual switch called “motion lights”. If this is turned on, it enables motion activated lighting. It’s based on a schedule (sunset-sunrise) and Alexa controllable.
I created a WebCore Piston to do the following (short version):
If the light is off and motion is detected - turn the light on
If the light is on or another light in that room is on - do nothing
If the light is turn on by motion and no more motion is detected - turn off light
if light is turned on by motion but user changes the light level (dimmer), that light is now in manual mode. Motion will work again once the light is turned off.
If my AV receiver is on, disable motion lighting for that room.
Your about to hit the tip of the iceburg!!!
The following article is from 2017, but still applies and has a lot of good information on Z wave sensors:
A quick point, if you go with the ST Zigbee motion sensor and need a relay, keep in mind IKEA’s Tradfri line is also Zigbee. Their smart plugs are $10. I have one I mainly added for this exact reason (and found an additional use for it, too). With a ST hub you don’t need the IKEA hub, they join directly.
Yes I have the Lutron Bridge. When ogiewon first suggested Samsung’s Zigbee motion sensor I wasn’t sure I wanted to go with Zigbee since I already have a couple of Z-Wave devices. Also he mentioned I might have to spend more money and strengthen the mesh network by buying a $32 Zigbee repeater.
Chris_Laudermilk’s post kind of changed my mind though where you could buy a $10 IKEA Tradfri Zigbee Smart Plug to use as a repeater… I like that idea!
I’m assuming the Samsung SmartThing motion sensor is decent or it wouldn’t have been mentioned here. Since my Caseta switches are On/Off switches not dimmers what will be my programming options… will it basically be to set motion sensor sensitivity? Can you program the sensor to only activate during certain hours of the day?
This will be mounted in a hallway to activate a light whenever anyone walks through. Should this be mounted high on the wall close to the ceiling?
My entire house is also Caseta and I have motion sensors in most rooms -except bathrooms-. My sensors are Smartthings and they work well with Caseta. There is a small lag (.5 to 1 second) but this is also true with most sensors that are internet based. The ST sensor is very versatile (the base is a metallic ball that you attach anywhere and the sensor has a magnetic depression that moves around this ball so it is very easy to change horizontal and vertical angles, adjust range, etc.). They also report temperature. In my experience they work best when the movement is across rather than frontal so I would recommend you put them high in a corner or above.
I also have few hidden Ikea Tradfi Zigbee plugs/repeaters but you should know they are $10 and for a reason. They are huge eyesores (but they don’t block the second outlet, ST one does block th esecond outlet), they have no manual switch (unlike the Smartthings one), and feel very cheap (again, unlike the Smartthings one, which feels like an Apple plug ha ha). BUt they are very good plug/repeaters and you can buy 3 for the price of one ST plug.
Very good point. 
This comes up all the time. People think a motion sensor is like a camera so they should point it straight on at where they expect the motion to come from, but they actually measure changes that pass 90° to the sensor. Sometimes people think they have a laggy sensor when in fact the issue was just the placement.
There are more details in the community FAQ:
CarlMN thanks for explaining the Tradfi Zigbee plugs/repeaters just so I’ll know what I’m getting. I suppose if it’s hidden it would be ok but if out in the open maybe the ST plug would be best.
I’m getting ready to order the ST sensor and I’ll try mounting it up high and see how I get along.
Ok I got my SmartThings motion sensor today and it is connected to the ST app… I also have my Caseta light switch connected to the ST’s app.
So now that they both show up in the ST’s app but how do I link the Caseta switch to the motion sensor?
Once I link them together how can I program it so the motion sensor doesn’t trigger say between 11:00 PM - 6:00 AM?
Within the Smartthing app on the left menu choose smart apps then smart lightning and create a new light automation. Just follow the guided steps it’s very easy. It will ask you which lights you want to control, what sensors you want to use, when, etc.
Once you link Caseta switches with Smartthings, the lights are fully integrated with most Smartthings compatible Things.
Thanks CarlMN that worked I’ll just have to play with positioning the sensor over the weekend.
Now how can I program it not to trigger during certain hours?
Yes of course. After you choose which motion sensor you want to use, etc there is a little arrow you have to click which will give you more options (see attached pic)…
Gosh that was too simple how did I miss that! 
I’ve been messing with this some this morning trying to find the right location. Can anyone tell me if the 3M two-sided tape on the back of the mount will pull away Sheetrock or paint if you need to remove it?
That is very possible. I use 3M Command Strips as they are easy to remove without damaging the wall.
It may damage the paint,. The longer the tape has been in place the more likely it will come out with paint.
