How SAR varies
The SAR from a mobile phone varies considerably during use due to adaptive power control and the connection back to the mobile network. A maximum SAR value does not provide sufficient information about the amount of RF exposure under typical usage conditions to reliably compare individual cell phone models. The level of exposure depends on the distance between the person and the mobile and the amount of RF power the mobile transmits.
Mobile devices will attempt to use the minimum amount of energy to provide a reliable service quality while at the same time preserve battery life, actual exposure varies continually depending on a range of factors:
- The distance between the person and the mobile device
RF fields are much weaker even a short distance from a mobile. Keeping the mobile away from the body by using an earpiece or loudspeaker function will significantly reduce exposure.
- The distance from the base station
RF EMF from a mobile phone will vary its power level depending on its proximity to a base station using automatic power control. The closer it is to a base station, the less power is required - the further away it is, the more power is required (up to the phones maximum SAR).
- Obstacles between the user and the base station
If there is a building, walls, hills, trees or other obstruction between the mobile and the base station, the signal received by base station may also be weaker meaning the RF field strength from the mobile must increase so it can still communicate with the base station.
- The service being used
Making a voice call from a mobile phone could lead to greater exposure than texts, emails, pictures, web, TV and downloads. This is because voice calls are generally made with the mobile phone next to the head, while it is held away from the body when sending texts and emails and watching TV. Calls may also take longer than sending texts and emails, again increasing exposure. The time taken to write a text or email or reviewing information already stored on your mobile phone will not result in any significant exposure.
Exposure is related to actual communications with the network, such as during the sending of a message or continuously during a voice call. These higher levels of exposure as a result of a voice call are still less than the ICNIRP guidelines because all phones must comply with international safety standards (see section 5: Relevant standards).
Mobile phones are also designed to use the lowest possible power to connect to the nearest base station and automatically adjust the power depending on the environment.