Methods and systems of providing enhanced security to an access-controlled area are disclosed herein. In one implementation a user device generates a signal from which features are extracted to generate a device fingerprint. The features of the signal may be rare, or in some cases unique, to a particular user device such that the use of user device with a known device fingerprint may thwart a relay attack on the access-controlled area. The features of the signal may be related to manufacturing variations between user devices, even devices of the same model. The variations may be related to variations in an electro-mechanical structure of a motion sensor between two user devices. The variations in the electro-mechanical structure may cause variations in a capacitance sensed by the motion sensor. Features of the signal may be analyzed in the frequency or time domains to generate the device fingerprint.