You have neatly mounted a Bluetooth BLE sensor on your trailer. Everything seems fine, but in the app there is... nothing. No signal, no data. Sound familiar? For many agricultural customers, this is a frustrating experience — and the cause is almost always the same: the sensor is hidden in a closed metal box.
In this article, we explain in simple terms why this is a problem and what you can do to solve it.
What is a BLE sensor?
BLE stands for Bluetooth Low Energy —a wireless technology that transmits small amounts of data over short distances. Our sensors use BLE to send information such as temperature, location, or motion to your vehicle’s onboard computer. The main advantage: low power consumption and long battery life. The downside: the signal is susceptible to obstacles.
Metal blocks the BLE signal
BLE operates on a radio frequency of 2.4 GHz. These radio waves are invisible, but they do behave in a physical way—just like light that hits a wall. To radio waves, metal acts as both an impenetrable wall and a mirror.
As soon as a BLE sensor is placed in a closed metal box, three things happen simultaneously:
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1
Reflection The signal bounces off the inner walls of the box and cannot escape.
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2
Absorption The metal absorbs part of the signal energy, causing the signal to quickly attenuate.
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3
Antenna interference The proximity of metal interferes with the sensor's own antenna, causing it to transmit over an even shorter range.
And what effect does concrete have on the BLE signal?
Concrete structures also pose a problem for BLE signals. Concrete significantly attenuates the 2.4 GHz frequency—a thick concrete wall can weaken the signal by more than 99%. Reinforced concrete (containing steel reinforcement) acts as a complete barrier, because the steel bars function as a sort of metal grid—again, a Faraday-like effect.
Faraday's cage
A sealed metal enclosure blocks all electromagnetic signals from entering or leaving. Radio waves—such as BLE at 2.4 GHz—cannot get in or out.
Your sensor is, as it were, trapped in a quiet, enclosed space.
How to Install a BLE Sensor Correctly
Fortunately, there are simple solutions. Here are the most important points to consider when installing your BLE sensor:
Mount on the outside
Attach the BLE sensor to the outside of the asset. For a trailer, it should preferably be mounted at the front or on the side—but always facing forward, toward the receiver.
As high as possible, with as few obstacles as possible
Place the BLE sensor as high as possible on the asset, and as close as possible to the receiver (the towing vehicle), with as few obstacles in between as possible.
Test the signal before final installation
To ensure that your BLE sensor is properly positioned relative to the receiver, it’s best to test the signal in the app before final installation.
Check out our solutions for tracking trailers and non-powered equipment:
In a nutshell — proper use of BLE sensors
A BLE sensor in a metal box is like a person whispering from a hermetically sealed room—no one can hear it. Faraday's cage prevents radio waves from passing through metal. Always mount your sensor in a visible location, outside of metal enclosures, and with a clear line of sight to the on-board computer.
Frequently Asked Questions
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Metal acts as a Faraday cage: it reflects, absorbs, and disrupts the 2.4 GHz Bluetooth signal. Radio waves cannot escape from an enclosed metal structure. The sensor is, as it were, trapped in a shielded space with no connection to the outside world.
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Yes. Concrete significantly attenuates the 2.4 GHz frequency. A thick concrete wall can weaken the signal by more than 99%. Reinforced concrete (with steel reinforcement) acts like a metal grid and has the same Faraday-cage effect as a closed metal box.
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Attach the sensor to the outside of the vehicle—on a trailer, preferably at the front or on the side, always facing forward toward the receiver. Mount it as high as possible, with as few obstacles as possible between the sensor and the onboard computer. Test the signal in the app before final installation.
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BLE stands for Bluetooth Low Energy —a wireless technology that transmits small amounts of data over short distances. AllConnects sensors use BLE to send information such as temperature, location, or motion to the onboard computer. Advantage: low power consumption, long battery life. Disadvantage: the signal is susceptible to obstacles such as metal and concrete.
Questions about BLE Bluetooth technology for your assets?
Whether it’s trailers, semi-trailers, agricultural machinery, or other equipment—our team will help you ensure proper installation and choose the right solution for your situation.
Hilde Lavrijssen
Marketing Manager — AllConnects BV
Hilde closely follows Belgian legislation on mobility, fleet management, and time tracking and translates it into practical insights for companies in the transportation industry.
