Beam break sensors create a light beam and provide a signal when this light beam has been broken by an object. Typically they have a transmitter and a receiver part. In most cases the light beam is in the infra-red part of the spectrum, making in invisible to the eye. Some sensors also use a laser.
Beam break sensors are useful in the smart home for occupancy detection and to create "virtual doors" and zones, within rooms or other zones. An archway between rooms is a good example of where a beam break sensor can create a virtual door between spaces.
Beam break sensors come in many form factors and with varying specifications. One of the key features is the range at which they operate. Small, cheap beam break sensors typically only operate over a short range (less than 25cm). Most operate over a distance of a few meters and some of the more powerful ones will have a range over 10m. Those using a laser or another kind of powerful, focussed beam will have a range of 25m or more. When used outside though, the range will be reduced by rain, fog and snow. We have seen sensors with a claimed 100m range.
Reflective beam break sensors typically have only one active component to install (which can be a major advantage). This incorporates both the transmitter and the receiver and uses a (passive) mirror or reflector, to bounce the light beam back.
Because beam break sensors are continually using power to create a persistent beam (most are actually a high frequency pulse train), few are battery powered and wireless. All of the sensors we have used require a wired connection and an external power supply. The longer the range, the more power they typically consume.
Our contextual smart home models beam break sensors as a type called 'Beam'. They therefore inherit all of our smart home's common capabilities and can generate notifications, voice announcements, etc. They can also be queried by any other element of our smart home and used for intelligent automation by controllers. They have two states, either 'Open' (beam broken) or 'Closed' (beam intact) and each change of state is sent to our Home Control System as an encrypted event.
The model also supports timeouts, so we can define a duration for being notified when the beam has been 'Open' for more than 30 seconds (for example). This is useful to let us know if something has been left blocking the beam by accident.
We use a beam break sensor at one end of the path along the side of our house. Combined with the side gate at the other end, we can know if this path is occupied and use it to intelligently control lighting and for security applications. These ones are available on Amazon for around £8. They are wired and require a 12V dc power supply and have an internal relay to switch other voltages. The claimed range is up to 15m but we use them with a 1.5m gap.
Our @smartest_home will occasionally tweet activity from our side path beam break sensor.
