One question that often comes up is whether Bluetooth signals can go through walls. The answer is a bit more nuanced than a simple yes or no.
Bluetooth operates on a 2.4 GHz ISM (Industrial, Scientific, and Medical) radio frequency band. This frequency is also shared by other wireless technologies like Wi-Fi. Bluetooth signals are designed to be robust but are generally short-range, typically extending up to 50 metres. As it uses the same frequency as Wi-Fi which most people have a knowledge of range of, a very rough approximation is to think of Bluetooth as being similar to Wi-Fi.
The material of the wall plays a significant role in how well a Bluetooth signal can pass through it. Materials like drywall, glass and wood are generally more permeable to Bluetooth signals. In contrast, concrete, brick and metal can severely limit or block the signal altogether.
The strength of the Bluetooth signal also matters. Higher-powered Bluetooth devices can transmit signals that are more likely to pass through walls. However, even with a strong signal, the quality may degrade as it passes through obstacles.
The distance between the transmitting and receiving devices will also impact the signal’s ability to pass through walls. The closer the devices are to each other, the more likely it is that the signal will successfully penetrate the wall.
In practical terms, while it’s possible for Bluetooth signals to go through walls, the quality and reliability of the connection can be compromised.
So, does Bluetooth signal go through walls? The answer is yes, but with caveats. The type of wall, the strength of the signal, interference from other devices, and the distance between the connected devices all play a role in determining how well a Bluetooth signal can penetrate walls.
Many people inquire about adjusting the transmission distance of a beacon. They often wish to either conserve battery or restrict the range at which a beacon is detectable.
While some third-party platforms and SDKs offer distance settings, it’s a misconception to think you can directly set the distance. What you’re actually adjusting is the transmission power, which in turn influences the transmission distance. But since this involves radio waves, which are prone to reflections and interference, it’s impossible to guarantee that a specific power will equate to a precise distance.
When using an app to detect beacons, you can employ the Received Signal Strength Indicator (RSSI) to focus on those within a desired range. However, it’s challenging to precisely correlate RSSI with the actual distance.
Some wonder if they can set the distance in terms of centimetres, similar to NFC. Typically, this isn’t feasible because even at their lowest power setting, most beacons transmit over a distance of about a metre.
Rather than asking if the transmitter’s distance can be minimised, it might be more practical to configure the receiver to disregard detections from further away. By using the RSSI value on the receiving app or another Bluetooth scanning device, you can filter out distant beacons. Specifically, you can dismiss detections with an RSSI below a certain threshold, allowing you to focus on detections within a centimetre range.
A critical aspect of beacon setup is the transmission power (Tx power) setting, which determines the range of communication and the beacon battery consumption. The Tx power is measured in dBm (Decibel-milliwatt) and indicates the strength of the radio signal. The standard range of TX power settings typically falls within -30 dBm to +4 dBm, the ‘standard’ level being 0dBm.
Lower TX power settings, between less than 0 dBm, are used for short-range. Low power settings conserve battery life by minimizing energy consumption, making them ideal for battery-powered beacons. Higher power settings, above 0 dBm are used for long-range communications. However, it is important to note that higher power settings significantly impact battery life.
A change in ± 3dBm is a halving or doubling of power. An approximate rule of thumb is that this halving/doubling affects the battery in opposite way way. For example, going from 0dBm to -3dBm will approximately double the battery life. This is a very rough approximation because the beacon also uses a small amount of power when not transmitting, which is most of the time because the beacon only transmits for a few milliseconds (ms) every configurable 100ms to 10 sec.
A change in ± 3dBm doesn’t halve or double the range. Instead, the range approximately follows inverse square law with distance. Again this is approximate due to antenna characteristics, obstructions and interference. Signal processing at the receiver can also optimise performance and improve on the usable range.
Our recommendation is to start off with the ‘standard’ level of 0dBm. This will provide the battery life quoted by the manufacturer. If you really need more range then increase the power. If the range is further than you require then reduce the power to obtain a better battery life. You can test the range and received radio level using nRF Connect app on a smartphone.
Too many potential customers contact us asking what’s the least expensive beacon that provides the best range, the best battery life and the smallest size. Unfortunately, all these things are related. You need a larger battery to provide enough power for a longer range. A large battery implies a larger beacon size. A larger battery and case implies a more expensive beacon. The choice of ‘best’ beacon usually involves some sort of compromise.
It’s also often the case that customers focus on price, range, battery life and size without considering other factors such as:
Visual appearance – Good-looking beacons can sometimes be counter-productive as they can be attractive to thieves.
App – Some manufacturer configuration apps are easier to use than others.
Waterproofing – Some unexpected scenarios need waterproofing due to high humidity.
Motion triggering – Some beacons provide motion triggering to significantly increase battery life.
On-off button – It’s sometimes desirable to be able to turn the beacon on and off without having to remove the battery.
Attachment options – Some beacons include strong double sided stickers, tabs for screws or holes for fastening.
Beacons allow you to set the transmit power to levels such as -30dBm, -20dBm, -16dBm, -12dBm, -8dBm, -4dBm, 0dBm and +4dBm. The number of actual setting values depends on the beacon. 0dbm is the default power recommended for normal use. Our article on Choosing the Transmitted Power explains these values and how they relate to distance.
We are often asked ‘What are the Estimated Distance/s for Tx Powers?’. This depends on the beacon, the environment and the receiver. An analogy is someone shouting a word. How loud does someone have to shout to be heard a certain distance? It depends on how clear the person shouts, how much noise there is and how well the person listening can hear. With beacons it depends on the beacon (mainly antenna) design, how much radio frequency (RF) noise there is, the degree of RF reflections, the receiving ability of the device (smartphone or gateway) you are using and even the weather.
The only way to determine the relationship between distance and power is experimentally and it will likely change over time as the environment changes.
Most beacons’ configuration app have a setting for iBeacon ‘measured power’ or ‘RSSI at 1m’. This doesn’t change the power output by the beacon. Instead, it’s a value that’s put into the advertising data that declares to receiving devices what the power should be at a distance of 1 meter from the beacon. Receiving devices such as smartphones and gateways can use this to help calibrate a calculation to determine the rough distance from the beacon.
You don’t usually change this value and it’s actually rarely used. In most cases the value is irrelevant and can be ignored. However, if your app or receiving device does use this value, it’s best to first do some tests to see what the power level is in your particular situation. Things like the physical environment, blocking and beacon orientation can affect the actual power level at 1m. Set the value according to your particular scenario.
Beacons are often placed in shops, offices and other buildings for detection in smartphone apps. Battery powered beacons last from months to years depending on the size of the battery and the transmission power (adjustable). The compromise between battery life and physical range can be avoided if USB beacons are used instead.
USB beacons are powered from an available wallsocket, laptop, desktop or other standard USB socket. Alternatively, they can be powered using an inexpensive mains charger used to charge a smartphone or other device. Powering from the mains allows the beacon to be permanently set to full power with no worry about checking or changing the battery.
The use of mains power also allows for use of specialist beacons that output the maximium legally allowed (Class 1) power that wouldn’t be feasible using battery power.
The FSC-BP109 can be received up to 1000m on Android and 4000m on iOS.
It’s an electronic component to be used at the SoC output to amplify the signal prior to being sent to the antenna. We expect this to be included in some future long range beacon designs. However, note that it uses more current (115 mA at +20 dBm) so is less suitable for use in coin-cell based battery powered designs.
Our ultra long range beacons already use RF amplifiers but from different component manufacturers. For example the iB003N-PA uses a RFAXIS X2401C chip to achieve up to 300m range. The FSC-BP109 also uses an output amplifier to reach up to 1000m on Android and 4000m on iOS but this beacon requires USB power.
Unseen Tech has a recent whitepaper on Bluetooth 5 range. It describes some tests that were performed to assess Bluetooth 5 to see the improvements in range compared to Bluetooth 4’s typical 30m to 100m. The tests used development boards from Texas Instruments and Nordic that, used outside, achieved about 650m and 750m respectively.
While some companies are claiming Bluetooth 5 support in products, many don’t actually use Bluetooth 5 yet but instead offer an upgrade path to Bluetooth 5. Other’s do offer Bluetooth 5 but downgrade to Bluetooth 4 when communicating with Bluetooth 4 devices (e.g. smartphones) which are still the large majority of devices.