A semi-passive tags operate similarly to passive RFID tags. However, they contain a battery that enables longer reading distance and also enables the tag to operate independently of the reader. One example is a data logger tag, which can take sensor readings automatically and run a real-time clock. Such as tag can be scanned using a standard RFID reader. Semi-passive tag modules are also often used as a communications interface to other devices and sensors or even a mobile phone. It is important to understand that the communication in semi-passive tags is still completely passive; no power is transmitted – the tag simply reflects back some of the power emitted by the RFID reader.