5 Pack NC Magnetic Door Contacts Switch Sensor for Home Alarm System

I purchased these to replace a sticking alarm sensor I have on a door. The sensor is installed in the door frame/jamb and the magnet is installed in the door.These are actually metric. They do say 3/8 and for practical purposes they will work with a 3/8" hole but you may have to open it up a bit. 10mm is actually 25/64" or about a 64th of an inch larger than 3/8". They are not tapered. The black part is a little smaller than 10mm then the white plug is 10mm with tapered splines at the top that flare out to 11.5mm or 7/16 which is designed to lock it into the wood. There is a 12mm or 15/32" flange at the top that is about 1/64" thick. In soft pine you could probably hammer it flat but if you are working on oak or another hard wood you need to open the hole up and recess if you don't want that flange sticking up.I tested the open and close and when in line coming together the switch trips at about 15mm or almost 5/8" which is pretty good. As long as you keep the gap between the top of door and bottom of frame less than 1/2" you should be ok. Alignment of the magnets to each other when the door is closed is also important. I placed the magnets so that when closed there would be 1/16" gap between them. As you bring them towards each other like the action of a closing door, the switch closes as soon as the magnet begins to overlap the switch. So, you could be as much as 10mm or about 3/8" off of alignment and the switch will still close. This means that as the door sags, swells or warps you have a tolerance to work with that is pretty good.If you have an issue with the switch not closing because the magnet is not aligned you can alternatively use a wafer 1/16" thick neodymium magnet on top of the door in the proper place with a drop of crazy glue.While these are nice because they are hidden in the door and frame they are more easily defeated. Since the gap between the two is accessible from outside you could defeat them by putting a wafer magnet on a piece of blue tape and slipping it in the gap where the sensor is then pressing the tape to the frame to keep the sensor closed when the door magnet is removed. The magnet will actually stick to the sensor they are so strong but using the tape allows you to position it with the interference of the door's magnet. This is why it is a good idea to slightly recess and skim coat the sensor to conceal its location.I discovered this while working on a house. We had to remove two French doors that were part of a larger alarm circuit. So that we did not have to bypass the whole circuit we just placed some neodymium wafer magnets on the sensors and they stayed in place bypassing those individual sensors. When the alarm guy passed by one day I asked him about it and how easy it would be to defeat from outside and he said it would not work. We tested it and I was able to simply slip the magnet in on a piece of blue tape and defeated the sensor. His response was that I was lucky because if I had flipped the magnet to the other side it would have not worked. I didn't bother testing but told him I had a 50/50 chance and if the alarm had gone off I would just walk away having not broken in and return the next day with the magnet flipped...If you need this style sensor these work well. Just be aware they are metric and may be a little snug.

I've been looking for some sort of electromagnetic switch to mount somewhere on my overhead garage door to indicate when it's open. The way our house and attached garage is configured, if I'm in the house, I can't tell if the garage door is up / open. Several times I've accidently left it up all night long, which is a stupid thing to do, even in a relatively safe neighborhood. I put together a little unit with a 24 VAC transformer and relay, which is connected between the garage door and warning light mounted above the entry door for the garage. All I needed was a switch that is activated when the door is up, i.e., when the two parts of the switch are separated from each other, to turn on the warning light. My plan is to install one or two of these little switch parts in small blocks of wood, one attached to the moving door and the other on one of the fixed rails adjacent to door. After I get them mounted, I'll update this with a picture.

These magnetic switches have a lot of potential uses. The doors and windows in my home have them embedded in support of a wired security system. Beyond that they can be useful for position sensing, for example with model trains. That's my planned use with these. The parts are well constructed. They're solid. They're reasonably sized. They're tapered so that when you insert them in a door/window, if you drilled the hole right, they should stay put. My only gripe about the construction quality is that I found two out of ten screws (on the five switch parts) were hard to turn. Turning (opening) one of those two felt like I was very close to stripping out the Philips head, even though my screwdriver was the right size. It's not clear to me why this problem existed. Everything else about these magnetic switches works well. I've attached a photo of a test setup where I determined the distance at which a switch would close. In my photo you can see the magnet is about 13mm from the face of the switch. That's where my Fluke meter started indicating the circuit had closed. On repeated tests I observed closing distances of 12 to 15mm. The claimed half inch operating distance would be 12.7mm so in general this switch is operating according to spec. Overall, except for the problem with the two screws, I find these switches useful and well done.

These are effective little sensors that get drilled into a door frame and the door in order to detect if its open. Rather simply, you drill a hole on both sides, push the sensor in, and the circuit will close when the magnet is near / the door is closed. It has a pretty wide tolerance, closing the circuit if the magnet is within ~1 inch. Resistance when the door is open is near infinity and very low when the door is closed, so the sensor behaves effectively. You'd generally wire this to a security system, or if you're DIYing the system, you'd run a GPIO with a pull-up through the detector and to ground, and detect the input behavior (when the door is closed, the GPIO will read low, etc).It's important to note that these don't have a really good mounting solution besides being drilled into a hole, so unless you're clever, note that you're going to need to drill into the door and walls to install these.

These are nice magnetic switches. I have a lot of electronic projects and having a good easy to use switch is a blessing. These switches come with some strong magnets that can be placed a small distance away from the switch to activate it (1.5 cm or .6 inches). I have had other switches that being right next to the magnet may or may not activate the switch. I use these switches with my raspberry pi projects with no problem. I can quickly check, whether I am local and or across the country, to make sure all monitored doors/windows are closed or be alerted when the switch loses contact with the magnet. Price for me was good and I would recommend this product.