Battery-Powered Contact Sensor Features
There are many different brands of battery-powered contact sensors, operating on many different protocols. There are zigbee ones that use the Zigbee home automation profile and work directly with SmartThings. There are proprietary Zigbee sensors which cannot talk directly to SmartThings. There are zwave versions. There are security system versions using 433 MHz which cannot talk directly to smart things.
Sometimes a manufacturer will make identical-looking ones in several different protocols, so you have to read very carefully to make sure you get the one you want.
It’s also really common that someone moves into a house that already has sensors set up from a previous security system that they want to try to use with smart things.
It is sometimes, but not Always, possible to rig some kind of integration with some of these legacy sensors. You will find topics in the forum that discuss that. It’s not necessarily easy and may require additional hardware pieces.
All of these are often called “door and window sensors.”
For the rest of this note, I am only going to discuss sensors that can be integrated directly with smartthings. So that means zigbee home automation profile, zwave, or sensors like the kumostat wireless tag which have a cloud to cloud interface.
Pretty much all of the sensors are what are called “magnetic reed” sensors. These have a thin piece of metal (the reed) which gets pulled by a magnet to close a contact.
These sensors vary hugely in build quality. Cheaper ones have less powerful magnets, cheaper cases, flimsy battery holders. They can be very finicky in getting the magnet placed in exactly the right position to close the circuit. They’re still usable for many purposes, but it’s important to understand why one sensor might be $17 and another one might be $40.
If you intend to try to use a sensor outdoors (in a sheltered position) or on something that has more of a gap, you will probably want one of the more expensive higher-quality builds.
If you just want one on a cabinet door, a cheaper one may be fine.
As always, Z wave plus will have a longer range then older zwave.
Zigbee sensors tend to be smaller with better battery life. Zigbee also tends to transmit better through rain, so if it is often chosen for sensors which are transmitting in outdoor spaces, for example to report if shed door was left open.
And Z wave is limited to four hops per message while Zigbee can do up to 30 which means if you have a really big house or if you have a lot of architectural features that you need to bounce signal around, zigbee might be better.
But then we always come back to the Wi-Fi issue. Wi-Fi doesn’t interfere with Z wave, and it sometimes can with zigbee. So a lot of people just find zwave easier to work with as long as the maximum distance from the hub is no more than 200 feet.
There are two common forms. Surface-mount have two rectangular pieces, one with the radio and the reed and one with the magnet.
Embedded have a tube that goes inside the wall and a small contact piece for the other side.
Triangle shaped window sensors have become more popular in 2016, and are intended to be a little bit less bulky. They are normally less than half an inch tall and are intended to fit in the corner of the window. Aeotec makes a popular version.
Sensative has just released a new line of very thin strip sensors which are nearly invisible on the door. They are weatherproof and can be painted.
These days many sensors include a temperature sensor as well. Some even have a lux sensor also. However a cheap contact sensor probably has a cheap temperature sensor so it’s pretty common for these temperatures to be off by five or 7°.
Some models have “dry contacts” which are unused electrical contacts inside the sensor case. This allows you to wire other devices to them, in effect adding A Zwave or Zigbee radio to the other device. Some typical projects utilizing this would be pressure mats or doorbells. If you’re going to do this, you’re probably buying the contact sensor for that specific project, so you can investigate model options at that time.
Aeotec has several different models in different shapes with different features, including a tubular model intended to go into the wall, the thin triangular model for window corners, and a regular rectangular style. All have different features and are quite popular.
Fibaro sensors come in several different colors and have a good quality temperature sensor.
The PEQ sensors sold At Best Buy are excellent Quality, and occasionally go on sale for $20 a sensor which is an excellent price.
Lowes iris devices come in two generations. The first generation is not compatible with SmartThings. The second generation, which uses the zigbee home automation profile, is. These are quite inexpensive and include a temperature sensor, although there are a number of forum reports that the temperature is not very accurate. Some community members have also reported that they seem to go through batteries very quickly.
NYCE sensors. Again, the first generation is not compatible with smart things. The one that uses the zigbee home automation profile is. These are very small.
Kumostat wireless tags. These do not connect directly to smart things, but there is a cloud to cloud integration or you can use IFTTT. They are significant because they have a much longer range than Zigbee. Customer service on these is reportedly terrible, with people having a really hard time doing returns if they happen to get a bad device. But the general quality is good, and if you pay with a credit card you could have your credit card refuse to pay on a defective item. Search the forums for more information. You will need to buy their Ethernet manager as well as any individual tags. Most people won’t need to consider these, but they do fit the bill for some specific use cases. Reports temperature and humidity as well as open/close.
Sensative has a patent on their very thin strips which are intended to be invisible when the door is closed. These are particularly helpful for sliding glass doors where conventional contact sensors may not fit easily.
Xiaomi is a very large consumer electronics company in China that has their own home automation line. These are zigbee devices, but not certified for the zigbee home automation profile. However, a number of community members have verified that they do work with SmartThings, although the pairing process is pretty tedious. These devices are very inexpensive, typically about twelve dollars a sensor, and seem to be well engineered. They don’t have any frills like extra temperature or humidity sensors. And you may have to wait about a month for delivery. Gearbest will ship them to both the US and Europe. You don’t need the Xiaomi Gateway. The devices which have been verified to work are the contact sensor, the motion sensor (called the “human body sensor”), The humidity sensor, and the battery operated button.
All other brands are pretty similar, with the understanding that cheaper devices probably have lesser build quality and shorter warranties.