Bluetooth Low Energy for IoT

What BLE is and isn't

BLE was introduced in Bluetooth 4.0 (2010) and is largely independent from Bluetooth Classic. They share the brand and the 2.4 GHz band but use different radio modulation, different protocol stacks, and different application models. A device may support one, the other, or both ("dual-mode" / "BR/EDR + LE").

BLE design priorities:

• Very low power consumption — coin cell battery operation for months to years.
• Small data exchanges — kilobytes per transfer, not megabytes.
• Fast connection setup — milliseconds, not seconds.
• Simple stack — implementable in tiny microcontrollers.

Advertising and scanning

BLE devices have two roles:

• Advertiser (peripheral) — broadcasts packets on three or more advertising channels. Anyone listening can receive.
• Scanner (central) — listens for advertisements; may then initiate a connection.

Advertising packets are small (originally 31 bytes; BLE 5 extended to 255). They typically contain a device name, a few service UUIDs, and optional manufacturer-specific data. Many IoT devices operate entirely via advertising — a temperature sensor that broadcasts its reading every minute doesn't need any connection.

GATT: the data model

Once two devices connect, they speak GATT (Generic Attribute Profile). GATT defines a hierarchy:

Device
├── Service (collection of related characteristics)
│   ├── Characteristic (a single value with attributes)
│   │   └── Descriptor (metadata about the characteristic)
│   └── Characteristic
└── Service
    └── ...

Each service and characteristic has a UUID. Standard services are 16-bit UUIDs (Heart Rate Service is 0x180D). Custom services use 128-bit UUIDs to avoid collisions.

Operations on a characteristic:

• Read — central requests the value.
• Write — central sends a new value to the peripheral.
• Notify — peripheral pushes a value to the central without waiting for a read request.
• Indicate — like notify but with acknowledgment.

BLE 5 and extended features

Bluetooth 5 (2016) added several capabilities relevant to IoT:

• Long Range (coded PHY) — 4x the range at lower data rate.
• 2 Mbps PHY — double the data rate for shorter-range, higher-throughput applications.
• Extended advertising — 255-byte advertisements, on dedicated data channels, with separate scan responses.
• Periodic advertising — scheduled advertisements that scanners can synchronize to.
• Direction Finding (BLE 5.1) — angle-of-arrival/departure for indoor positioning.

Pairing and security

BLE pairing options:

"LE Secure Connections" (introduced in Bluetooth 4.2) uses ECDH for key exchange. Pre-4.2 LE Legacy Pairing is vulnerable to passive eavesdropping. Always require LE Secure Connections for new IoT designs.

BLE Mesh

BLE Mesh is a separate specification (not just BLE itself) that layers a multi-hop network on top of BLE advertising. Key features:

• Managed flooding. Messages propagate by being rebroadcast by nodes; smart caching prevents loops.
• Many-to-many. Lighting commands can address groups of nodes (e.g., "all lights in conference room A").
• Friend / low-power node pattern. Battery-powered nodes have "friend" nodes (mains-powered neighbors) that buffer messages for them so they can sleep.
• Application keys + network keys. Layered encryption similar to LoRaWAN's network/app split.

Used heavily in commercial lighting (Casambi, professional smart lighting) and increasingly in consumer smart home (alongside Matter).

Beacons

Beacons are BLE devices that only advertise — they never connect. The advertisement carries a small identifier. Phones or other scanners detect the beacon, identify it via the ID, and react.

• iBeacon (Apple) — UUID + major + minor. Used for proximity detection in retail, museums.
• Eddystone (Google, deprecated) — URL beacons that point at a web resource.
• AltBeacon — open spec for similar functionality.

BLE for sensor data

The common IoT pattern: a BLE peripheral (sensor) advertises continuously. A phone app or hub scans, connects when needed, reads characteristic values, disconnects. The sensor sleeps between advertisements.

For continuous sensors, the data path is:

Sensor → BLE → Hub / Phone → IP backhaul → Cloud → User app

BLE handles only the last-meter connectivity. The hub or phone is responsible for relaying data to the broader internet.

BLE vs Wi-Fi vs LoRaWAN for IoT

Frequently Asked Questions

What is Bluetooth Low Energy?

BLE is a wireless protocol designed for short-range, low-power communication, optimized for sending small amounts of data infrequently. Despite the name, it shares only the brand with Bluetooth Classic — the radio, protocol stack, and use cases are largely independent. BLE is the dominant standard for personal-area IoT: fitness trackers, beacons, smart home sensors, medical devices.

What is GATT?

Generic Attribute Profile — the data model BLE uses for structured exchange between devices. Each device exposes a hierarchy of services (collections), each service has characteristics (individual data points), and each characteristic can be read, written, or subscribed to for notifications. GATT replaces the more general (and less useful) ATT layer for most application development.

What is BLE advertising?

BLE devices broadcast small packets (up to 31 bytes pre-BLE-5, up to 255 bytes extended) without establishing a connection. Other devices scan for advertisements. Beacons (iBeacon, Eddystone) use advertising-only to broadcast their identity; scanners use it to discover devices to connect to. Advertising is one-way and stateless — many sensors operate entirely without ever connecting.

What is BLE Mesh?

A multi-hop networking layer on top of BLE that lets messages propagate through dozens or hundreds of nodes. Each node can relay messages for others, enabling whole-building lighting control, sensor networks, and large-scale deployments that exceed BLE's normal point-to-point range. BLE Mesh is a separate spec; not all BLE devices support it.

What is the typical range of BLE?

10-30 meters indoors with walls; 50-100 meters line-of-sight in optimal conditions. BLE 5 with Long Range mode extends this to several hundred meters by reducing data rate. Compare to LoRaWAN (kilometers, much lower data rate) and Wi-Fi (similar indoor range, much higher data rate and power).