A security device, comprising: a reader configured to read information stored on a credential device in a first operating mode, the reader being also configured to enter a second, sleep mode in which the reader consumes less power than in the first operating mode, the reader being further configured to enter the sleep mode after a predetermined period of inactivity wherein the reader is not reading a credential device or determining whether read information is valid; and a wake up module comprising an inductively coupled resonant circuit, the wake up module being configured to (i) detect the credential device near the reader if the credential device has a resonant frequency corresponding to a frequency of an electromagnetic field of the inductively coupled resonant circuit that is controlled by a stable oscillator circuit and (ii) provide an indication to wake up the reader from the sleep mode responsive to detecting a change of power in the electromagnetic field of the inductively coupled resonant circuit caused by the credential device, characterised in that the wake up module comprises first and second coils (42, 44), the first coil being adapted to provide the electromagnetic field and the second coil being adapted to detect when the credential device absorbs some of the electromagnetic field, the security device further comprises reader coils (102, 104) that are adapted to be used by the reader to receive credential information from the credential device, the first and second coils (42, 44) and the reader coils (102, 104) are supported on a single board, and the first coil is on one side of the board with the reader coils (102, 104) inside the first coil and the second coil is on a second, oppositely facing side of the board. a reader configured to read information stored on a credential device in a first operating mode, the reader being also configured to enter a second, sleep mode in which the reader consumes less power than in the first operating mode, the reader being further configured to enter the sleep mode after a predetermined period of inactivity wherein the reader is not reading a credential device or determining whether read information is valid; and a wake up module comprising an inductively coupled resonant circuit, the wake up module being configured to (i) detect the credential device near the reader if the credential device has a resonant frequency corresponding to a frequency of an electromagnetic field of the inductively coupled resonant circuit that is controlled by a stable oscillator circuit and (ii) provide an indication to wake up the reader from the sleep mode responsive to detecting a change of power in the electromagnetic field of the inductively coupled resonant circuit caused by the credential device, characterised in that the wake up module comprises first and second coils (42, 44), the first coil being adapted to provide the electromagnetic field and the second coil being adapted to detect when the credential device absorbs some of the electromagnetic field, the security device further comprises reader coils (102, 104) that are adapted to be used by the reader to receive credential information from the credential device, the first and second coils (42, 44) and the reader coils (102, 104) are supported on a single board, and the first coil is on one side of the board with the reader coils (102, 104) inside the first coil and the second coil is on a second, oppositely facing side of the board.