The device comprises an intrusion detection module (6), an image acquisition module (14), an energy management module (13) and an autonomous power source (9), the said detection module (6) being designed to furnish a detection signal having a first predetermined state when an intrusion is detected and a second predetermined state otherwise, and the said management module (13) being designed to make the said device change over from a waiting mode to a working mode by activating the supply of the image acquisition module (14) by the said autonomous power source (9) when the said signal changes over from the second state to the first state.The method includes a step consisting in furnishing the detection signal and, when the detection signal changes over from the second state to the first predetermined state, a step consisting in making the said device change over from the waiting mode to the working mode and a step consisting in achieving image acquisition.