BLE beacons in practice: protocols, sensors, layout and transmission power
A beacon is a small, battery-powered Bluetooth Low Energy transmitter. It is mounted on a wall, a ceiling or an object, or carried as an ID tag, and it broadcasts a short signal at intervals. A phone or a gateway that hears the signal can estimate how far away the beacon is. A deployment comes down to four decisions: which protocol the beacons speak, which sensors they carry, how they are laid out, and how strongly they transmit.
iBeacon or Eddystone
iBeacon and Eddystone are protocols: the formats in which a beacon broadcasts. Apple created iBeacon in 2013 and Google created Eddystone in 2015.
iBeacon is supported natively in iOS. Its main advantage is that it can wake an app: a customer does not have to open a store’s app before the app starts to receive the beacon’s signal. An iBeacon signal carries three pieces of information:
- a universally unique identifier (UUID), for the beacon’s general information
- a major identifier, for general location
- a minor identifier, for specific location
Eddystone is open: several companies worked on it, which makes it flexible and able to broadcast extra data, and it suits a wider range of operating systems. When this was written, Eddystone could send a URL to a Bluetooth device with no app in between. Its signal carries four kinds of information:
- a unique ID
- a URL, which sends the user to a web page
- telemetry (TLM): the beacon’s health and battery level, along with sensor data
- an ephemeral ID (EID): a short-lived, encrypted identifier that stops others from hijacking the beacon
Many manufacturers do not make the buyer choose, because their beacons speak both. Where a project is built around an app, iBeacon is the likelier fit. Where it has to reach people who have not installed one, Eddystone had the edge.
Sensors on board
A beacon can do more than announce itself. Manufacturers offer sensors as options, so it pays to settle the use case before ordering.
- Accelerometer. Measures motion and changes in velocity. On a production line it can detect a sudden fault and raise an alert. It can also tell whether an object is tilting or about to topple.
- Temperature sensor. Turns a beacon into a monitor for a cold chain, where medication must be kept at a set temperature.
- Ambient light sensor. Registers a door opening, a light switched on or a person passing. It can show that someone is in a room after hours, or drive the dimming of displays.
- Magnetometer. Senses magnetic fields, and can reveal a failure in equipment that depends on magnetization.
- Pressure sensor. Measures barometric pressure. A change in pressure inside a chamber can point to an equipment failure. In a wearable, it helps tell walking from climbing.
A point-based or a grid-based layout
Start from what the people in the space need: wayfinding, product information, touch-free payment. Then decide where to reach them: in a particular aisle, at one display, on the way in or on the way out. The answers lead to one of two layouts.
Point-based. Beacons sit at points of interest: a museum exhibit, a shelf, a theatre entrance. Coming near a beacon triggers something, such as a notification or a coupon. This layout needs fewer beacons than a grid, and it suits museums, venues, public spaces and retail shelves.
Grid-based. Beacons cover the space evenly, so an app can work out a person’s position by trilateration from three or more of them. A grid does more: indoor positioning, wayfinding, and analytics such as visitor counts, dwell times and interactions with beacons. The same infrastructure serves several purposes, which makes it the safer choice for a site that expects to add uses later. It is also more expensive and more complex.
Transmission power
Most beacons let you set their transmission (Tx) power, typically from around -30 dBm to +4 dBm.
dBm is the unit for the strength of a radio signal. A decibel expresses a power as a ratio to a reference value; the “m” says that the reference is 1 milliwatt. The scale is logarithmic:
- +3 dB doubles the power, and -3 dB halves it
- -6 dB is a quarter of the power, and -9 dB an eighth
- +10 dB is ten times the power
Signal strength falls with the square of the distance, so raising the power is an inefficient way to gain range. Power also drains the battery.
There are reasons to turn the power down. Lower power gives a smaller, more targeted zone, and keeps the zones of neighbouring beacons from overlapping. If a beacon should reach only the people within a metre of a display, a wide broadcast defeats the purpose.
There are also reasons to turn it up. A stronger signal leaves less margin for error when estimating the distance between devices. Where beacons are used to work out position, higher power is needed, and overlap between zones matters less.
Measured power. Many beacons carry a second value, the measured power: the signal strength (RSSI) a device should expect one metre from the beacon. It is there for calibration. Humid air carries a signal less well, so a site by the sea will see different values. People moving through the space affect it, since the human body is mostly water, and so do the building’s materials and layout. Measure the real signal at one metre on site and set the value to match. With a measured power that fits the environment, it becomes easier to estimate how many beacons the floor area needs. After that it rarely needs to change.
When a deployment misbehaves
The usual fixes in a new deployment are to power and spacing.
- Phones do not pick up a beacon. Raise its Tx power, or shorten its broadcast interval. A phone can also take around three seconds to notice a beacon in range.
- The wrong content shows, or none. Remove physical obstacles around the beacon, or raise its Tx power.
- Batteries run down sooner than expected. Lower the Tx power until an app sees no more than six beacons at once.
- The app reports an inaccurate position. Adjust the Tx power of the beacons, and check that the area is not crowded with too many of them.
- Overlapping beacons trigger more than one action. Lower their Tx power or mount them further apart.
Adapted in October 2026 from five articles first published on the Momentaj blog in 2017 and 2018. It describes the technology as it stood then.