IoT Sensors detect environmental and physical quantities and output them in the form of one or more numeric values.
Acceleration is detected using an accelerometer sensor that produces 3D x, y and z values. At rest, one of the values will be about 9.8 m/s that’s the affect of gravity. This can be used to determine orientation with respect to the ground. Acceleration data usually has to be sampled relatively frequently, every 100ms or less, to successfully interpret and distinguish been different types of movement. The high data rate means it’s only suitable for use with output protocols that can support high throughput. In many cases, data needs to be processed locally and only resultant detection signals sent up to the server/cloud. It’s for this reason some sensors only provide interpreted data such as motion or fall detection (see below).
Air pressure is measured in hPa and IoT sensors typically have a range of low hundreds to low thousands of hPa at and around normal air pressure. This be used to measure the current (weather) air pressure or can be used within enclosed spaces to detect the ambient pressure.
The dew point is the point at which air becomes saturated with water vapour. It’s the temperature air needs to be cooled to in order to achieve a relative humidity (RH) of 100%. It’s particularly useful for growers or aviators who need to know when dew or frost will form. It’s used by weather forecasters who need to know when weather will be uncomfortable.
Fall detection is a special case of use of an accelerometer to provide a binary falling/not falling indication. Local processing within the sensor detects a particular G force over a particular time.
This measures angular velocity as x y and z using the Coriolis effect. A gyroscope needs to oscillate at a high frequency which can be power hungry. Nearby vibrations can also create noise in the data. Data usually has to be sampled relatively frequently, every 100ms or less, to successfully interpret and distinguish been different types of movement. The high data rate means it’s only suitable for use with output protocols that can support high throughput. In many cases, data is processed locally and only resultant detection signals are sent up to the server/cloud.
Most IoT sensors measure humidity as relative humidity range in a range 0 to 100%. When used outside, humidity will usually be 100% when it is raining.
An IR sensor measures proximity, whether something is present or not, typically up to a change of 50cm. An Infra-red LED is used to reflect light off a detected object back to an Infra-red detector.
Light detectors tend to present integer values based on the lux light level. They tend to be uncalibrated due to the varying affect of mounting and casing. Values usually have to calibrated in subsequent software.
A magnet is usually detected using a hall effect switch or reed switch rather than with a magnetometer (see below). This produces an on/off value depending on whether a magnet is close by. The magnet can be placed on physical things to determine if they are close by or, for windows/doors, open or closed.
Magnetism is detected using a magnetometer sensor. Without any strong sources of magnetism nearby it will measure the Earth’s magnetic field as x, y and z values.
Motion is a special case of use of an accelerometer and on-board processing to produce a binary, moving or not moving indication.
This is an on/off sensor that detects when gas concentrations exceed a dangerous level, for example, 10% LEL.
Some sensors detect proximity through receiving a wireless signal containing an id of interest. For example, with Bluetooth, a detector might look for a Bluetooth MAC address or iBeacon UUID. See also IR and PIR.
IoT sensors are available that use a classic PIR sensor, as used in burglar alarms, to detect human presence as a binary occupied/not occupied indication.
IoT sensors are available that use a smoke sensor, as used in home alarms, to detect particles in the air as a binary smoke/no smoke indication.
Most IoT temperature sensors detect the ambient temperature in degrees celcius. Most sensor cases are not waterproof in order that the temperature (and humidity) quickly permeate to the electronic sensor. Some hold the actual sensor externally or externally via a probe so as to protect the electronics. Some processors within sensors have built in temperature sensors that track the processor temperature rather the ambient temperature. For low power devices, such as Bluetooth, the processor temperature will be close to the ambient temperature but as identified above, sealed cases hinder quick detection of changes of temperature.
Motion is a special case of use of an accelerometer and on-board processing to produce pitch and roll values in degrees.
Water detectors have external sensors that detect a change of electrical resistance brought about by the presence of water that’s presented as a binary water/no water indication.