How far can BLE transmit?

In a park early in the morning, an elderly person wearing a smart bracelet goes for a run, his phone simultaneously recording his steps and heart rate. In an office building, an employee uses a Bluetooth headset to answer calls, untethered by cables. In an industrial park, sensors transmit real-time device status data to a monitoring center via Bluetooth Low Energy (BLE). Behind these scenes lies a smart living network woven by BLE technology, utilizing short-range wireless connections. However, a common question lingers in users' minds: How far can BLE transmit? The answer lies in the balance between the device's "volume," "hearing," and environmental interference.

Transmitting Power

If BLE signals are like sound, then transmit power is the device's "volume." The louder the sound, the farther it travels, but it also consumes more power. BLE devices typically have several transmit power levels:

Low Power Mode (-20dBm to 0dBm): Similar to a whisper, with a transmission range of only about 10 meters. This is common in devices with small batteries, such as smart bracelets and headphones, sacrificing range in exchange for months or even years of battery life. For example, a certain brand of smart bracelet can operate continuously for 30 days in standard mode, but if it is set to maximum power transmission, the battery life is reduced to 3 days.

Medium power mode (4dBm to 8dBm): Equivalent to normal conversation, with a transmission range of 30-50 meters. Temperature and humidity sensors and smart light bulbs in smart homes often use this mode, providing coverage for a single room while maintaining battery life for months.

High power mode (10dBm to 20dBm): Like shouting, the theoretical range can exceed 100 meters, even reaching 300 meters in open air. Asset tracking tags in the industrial sector and soil monitoring equipment in agriculture often use high power mode to ensure signal penetration in complex environments such as farmland or warehouses.

The choice of transmit power is a trade-off between range and power consumption. For example, a logistics company used standard BLE tags to track goods, but metal shelving in the warehouse caused frequent signal loss. After switching to high-power tags, the transmission range increased to 150 meters, covering the entire warehouse, and the positioning error was reduced from 5 meters to 1 meter.

 

Receiver Sensitivity

Having loud volume alone isn't enough; a device also needs to be able to hear clearly. Receiver sensitivity reflects a device's ability to receive weak signals. The lower the value (e.g., -95dBm is more sensitive than -85dBm), the greater the distance the device can "hear."

High-sensitivity devices can detect extremely weak signals and maintain connections in complex environments, even at low transmit power.

Low-sensitivity devices have higher signal strength requirements and are prone to disconnection when transmit power is insufficient. Early BLE devices had low sensitivity, and in obstructed environments like offices, the actual range was often less than half of the nominal value.

Improving receive sensitivity relies on advances in chip technology. For example, the "Long Range Mode" (Coded PHY) introduced in the Bluetooth 5.0 standard reduces the data rate (from 1Mbps to 125kbps) in exchange for stronger interference immunity, improving receive sensitivity to -103dBm and extending the theoretical range from 100 meters to 400 meters.

 

Environmental Interference

Even if your device has a loud volume and excellent hearing, obstacles in the environment can still be invisible killers. Signals are reflected, scattered, and absorbed by obstacles during transmission, causing attenuation.

Open environments, such as outdoor playgrounds, offer virtually unobstructed signals, allowing high-power BLE devices to transmit over 300 meters. At a marathon, the organizing committee used high-power BLE beacons to cover a 42-kilometer course, allowing runners to receive real-time distance notifications on their phones.

Indoor environments: Walls and furniture can weaken the signal. In a typical office, the transmission range of a BLE device is typically reduced to 10-20 meters; if the walls are made of metal or concrete, the range can be further halved.

Special scenarios: Humid environments (such as bathrooms) accelerate signal attenuation, while areas with dense metal (such as elevators) can completely disrupt the signal.

Strategies for combating environmental interference include optimizing antenna design (such as using ceramic antennas to improve directivity), increasing deployment density (such as keeping indoor location beacons within 6-10 meters), or using mesh networking technology to extend coverage through relay nodes.

 

The "Elastic Boundary" of Distance

BLE's transmission range isn't a fixed value; it has an "elastic boundary" determined by transmit power, receive sensitivity, and the environment:

Consumer devices: Smartwatches, headphones, and other devices typically use low-power mode, with a range of approximately 10 meters, meeting daily usage requirements.

Smart home/industrial devices: Medium-power mode combined with high-sensitivity chips allows for ranges of up to 50-100 meters, covering homes or small factories.

Long-range applications: High-power devices combined with Bluetooth 5.0's long-range mode can reach over 1 kilometer in open environments. For example, an agricultural company uses BLE sensors to monitor temperature and humidity in farmland. The signal, after penetrating crops and simple sheds, can still communicate with the base station at a distance of 800 meters.

 

The extension of BLE's transmission range from 10 meters to 1 kilometer is not only an improvement in technical specifications, but also a precise response to user needs. Whether a smart bracelet remains connected to a phone during a morning run, industrial sensors transmit data reliably in a noisy workshop, or agricultural sensors transmit information across fields—behind these scenarios lies engineers' meticulous tuning of "volume," "hearing," and the environment.