A radio frequency (RF) device for authorizing user access to portions of a computer system. The RF device includes a power supply, processing circuitry that accesses the power supply according to a location of the RF device, and an antenna that transmits communication signals from the processing circuitry to a transponder that is coupled to the computer system. The processing circuitry is configured to operate at a first power level until the communication signals indicate that the location of the RF device is within a first range of the transponder. The processing circuitry is configured to begin operations at a second power level after the RF device is positioned within the first range of the transponder. The processing circuitry is also configured to operate at the second power level until the communication signals indicate that the location of the RF device has moved outside of a second range from the transponder.