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Home Automation Sensors - An Overview and Guide.


Sensors Put Your Home in the Know

Home automation is all about making your house smart. Just the same as with people, for a home to be smart it needs information. This information can come from you in the form of programs and commands, but often it will be collected directly by your home using sensors and used for automated functions. Sensors are therefore the foundation stone of any home automation system.

Because of this, the range and quality of the sensors you choose to install will determine what your home automation system is capable of doing and how effectively it operates.

In this article I will guide you through all of the most common sensors used in modern home automation systems, describing the technology and its most popular applications, as well as offering my own personal tips wherever I can.

Motion and Occupancy Sensors

One of the most popular sensor technologies for domestic automation systems is the motion detector. Often they will be put to multiple uses, such as triggering a burglar alarm if movement is detected when the house is supposed to be empty, or automatically switching lights on and off when you enter or leave a room.

The most common type of motion detector is the 'passive infrared sensor', or PIR. This works by detecting changes in infrared light radiation within its field of vision. When choosing a PIR it is important to make sure that the effective range is sufficient. Although most PIRs will easily be able to cover a room, larger rooms, especially in open plan design buildings may require more than one.

An occupancy or presence detector is basically the same technology as a regular motion sensor, but with a higher resolution. You can buy PIRs very cheaply, and they are still perfectly good for many applications - such as burglar alarms or controlling corridor lights. But if you want a system to be able to sense whether or not the living room is occupied, for example, so as to control the lighting and heating automatically, a cheap product will not be good enough. This is because they need movement to work, so if you are sitting still on your couch reading a book, the sensor may mistakenly send a signal to say that the room is empty. A presence or occupancy detector is able to identify the presence of a person in the room just from their breathing.

Tip: If you own pets then it may be a good idea for you to look for a product with adjustable sensitivity, so that you can manually find the right balance between operating correctly for humans, and not going off every time your cat walks past.

Presence Sensor Is Another Name for Occupancy Sensors

Light Sensors

A light sensor may also be known as a photosensor or photodiode. It is used to monitor the ambient light levels and report them back to your home automation controller. This is often used in conjunction with a motion or presence sensor to switch lights on automatically when someone enters a room - but only if they are needed. They can also be used to ensure that security lights only operate after dark, or make outdoor lighting come on automatically at dusk.

If you are using a light sensor outdoors then it is obviously important to ensure that you buy one with an appropriate weatherproof housing.

Temperature and Humidity Sensors

When temperature sensors are used they often come built into a thermostat unit or radiator actuator valve, but there are times when you may like to fit an independent thermometer. Small temperature sensors can easily be embedded into walls to avoid having more unsightly boxes stuck to your walls or ceiling.

Combined with a humidity sensor, they can be used to automatically control air conditioners or de-humidifiers, or even to automatically open windows if a room starts to get too 'muggy'.

Waterproof temperature sensors may be used outdoors, perhaps so that you can check whether your patio heater needs to be turned on before you go out, for example. They can also be used in tanks to monitor water temperature.

Tip:The placement of temperature sensors can significantly effect their operation. Ideally they should be located away from both doors and radiators, and somewhat down from the ceiling. If you notice that some rooms feel hotter than others when set to the same temperature, don't just think your mind is playing tricks on you - this is probably due to sensor placement. You don't necessarily need to move the sensor, however, if you are aware of the issue you can just change the temperature setting accordingly.

Multi Sensors

Because motion, light, temperature and humidity sensors are so commonly used together within home automation systems, some manufacturers package them up together into a single unit called a 'multi sensor'. Buying three or four pieces of kit bundled together like this can save money, and reduce the number of plastic boxes stuck to your ceilings and walls.

Fire Alarm Sensors

There are three main types of fire alarm sensors which are used in domestic properties:

  • Optical / Photoelectric: This is the most common type. It uses light beams, and the alarm is triggered if particles of smoke interrupt the beam.
  • Ionization: These detect ionized particles in the air, and are more sensitive that the optical type. This can mean, however, than it is more prone to false alarms than an optical sensor. Many modern systems use a combination of optical and ionization.
  • Heat: detects anomalous temperatures.

Tip: If you have an alarm which keeps going off when you are cooking then please do not just disconnected it and leave yourself unprotected. These false positives are due to the use of the wrong type of alarm for the location. Because many people do not even know that there are different types of fire alarm, it is quite common for the wrong type to be fitted in or around the kitchen - but remember that this is a high risk area and should absolutely not ever be left without a detector. The best type to use is a heat detector, as this will not be activated by smoke from frying things or burning toast, but can still detect fires in time to potentially save your life

Carbon Monoxide Sensors

Fire is not the only risk which you need to protect your family from. Hundreds of people die every year in the USA from Carbon Monoxide poisoning caused by faulty household appliances.

Carbon Monoxide is colourless, odourless, and can kill you without you even knowing that you are being poisoned. The symptoms include headache, dizziness, and nausea - all of which are commonly caused by a wide range of other things, meaning that victims may think they are just feeling a bit under the weather, go to lie down for a while, and never wake up.

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Tip:The most economical way to protect your family is to buy a combined carbon monoxide and fire alarm, but if this is not part of a home automation system with advanced notifications then make sure you memorize the different alarm sounds so you don't accidentally assume that you are getting a false positive from the fire alarm when it is actually the carbon monoxide alarm.

Flood and Leak Sensors

Flood or leak sensors are commonly fitted underneath baths and kitchen sinks, or in other locations with an elevated risk of leaks. If your plumbing does spring a leak then catching it early can save you a lot of trouble and expense, as water damage can have a major impact on your property.

A good quality flood / leak detector can sense the presence of even small leaks, and if connected to an actuator valve they can automatically shut off the water to prevent damage.

Using A Laser Pointer to Make a Tripwire Alarm

Proximity Sensors

In some systems proximity sensors are used in place of switches. This would allow the user to simply wave their hand over a wall mounted sensor to, for example, switch on the lights, rather than having to actually press a switch.

They can also be used in more advanced systems for a wide range of uses, from automatic cat-flaps to bird-feeder cameras.

Contact Sensors

Contact sensors are used for a range of applications, the most common of which is in burglary alarms. The sensor itself is basically just a kind of switch, which sends an electrical signal when two surfaces make contact. They can be used to monitor whether a door or window is open or closed.

Home security systems often use contact sensors in window frames, to trigger an alarm if a window is opened after the alarm has been activated. There are many other applications too, such as:

  • Automatically turning off the heating in a room if somebody opens a window, to save energy waste and make it easier to cool a room down.
  • If powered door systems are fitted you can check whether doors have been left open and close them from a remote location.
  • Switching on cupboard lights when you open the door.

Everspring Door and Window Contact Sensor

Glass Break Sensors

There are two different kinds of sensor which can detect an intruder breaking glass to enter your building.

The first type is installed on the window itself, limiting its usefulness for protecting an entire property. This is also known as a 'shock sensor' and is triggered by sudden high frequency vibrations when the glass it is attached to breaks.

The second type is basically a microphone tuned specifically to pick up the sound of breaking glass. This is more useful, because a single detector can cover even a relatively large room with many windows.

A Glass Break Sensor Installed Above Glass Panelled Doors


Energy Use Monitors

If you want to reduce your energy usage, for either environmental reasons, economic reasons, or both, then smart energy monitors are a 'must have' device. They can tell you exactly how much electricity each of your appliances, gadgets and electrical systems is using overall, and at any given time, empowering you with all the necessary knowledge to reduce your energy consumption. For example, you can use the information from your monitoring device to identify which devices you own use the most energy when left on standby, and then turn those specific devices off at the wall instead.

Most monitors fit between your socket and the appliance plug to monitor appliances individual, but you can also get whole house monitoring systems to track your overall energy use across the day.

Valta Energy Monitoring and Saving Starter Kit


In my opinion, one of the most enjoyable features that you can build into a home automation system is voice control. Even though voice recognition has been around for a while now, it still somehow feels futuristic and exciting to control your household electrics and electronics with voice commands.

Obviously if you want voice recognition features then you need microphones. The quality of the microphones you need for this purpose is not especially high, so there's no need to spend a fortune on pro quality products.

One interesting system which launched recently is CastleOS, which using the Kinnect system for Microsoft Xbox or Windows to detect and translate voice commands. Because the Kinnect is a high quality system this is very reliable and flexible, but if you want it to work in every room of a house you will have to buy a lot of Kinnects, which is going to get pretty expensive.

CastleOS & Microsoft Kinnect

Driveway Probes

A driveway probe is embedded into the driveway outside your home, and is then able to detect when a car is arriving or leaving. This information can be used by an automation system to open gates when you are leaving or to open a garage door, for example. It can also be used as part of an alarm system to begin recording if a vehicle arrives on your driveway, and then save the recording if your alarm is triggered within a certain period of time.

A Driveway Probe


Moisture Sensors

Moisture monitoring sensors are inexpensive and can be pushed into the soil in your garden or plant pots to monitor moisture levels and alert you when your plant needs to be watered.

Although there are advantages to buying a more high-tech version, a simple moisture sensor which works by measuring the resistance of the soil is so low-tech you can even make your own - check out this article for a step by step guide:

A variation on the moisture monitor is the water fill level sensor, which can be used in tanks and such like to monitor the level of water.

RFID Sensors

Radio Frequency Identification, or RFID, is wireless method for an electronic chip and sensor pair to exchange data. If you put aside your fears of government tagging and the big brother state and buy your own RFID chips and readers you can add a wide range of features to your home automation system.

The most common domestic use of RFID is to replace keys. Instead of a regular lock and key you have an electronic lock which opens when you wave your chip-containing card over the reader.

If you are willing to get a chip implanted into your body then things get a whole lot more advanced. Doors will open for you automatically when you approach. Your house will also know who is in which room and can customize its settings automatically; I remember reading an article about Bill Gate's home in which it described how RIFD was used to allow your favourite tunes to follow you around the house as background music.

Other Home Automation Technology Guides

© 2013 Dean Walsh


dhivya on January 19, 2017:

i need more details about upcoming home automation devices

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