Systems and methods for authenticating a user of a mobile communications device entail scanning an environment of the mobile device with a low power sensor and detecting a nearby person via the first sensor. In response, a higher power sensor is activated and the person is authenticated via the second sensor using a first authentication mechanism. A first level of access is granted to the person at this point. When the person moves to within a first threshold distance of the device, the person is authenticated using a second more secure authentication mechanism, and a second, higher, level of access is granted to the person.