A wireless sensor node is described. The wireless sensor node may include a wake-up circuitry configured to awaken the sensor when a request is received. The sensor may be placed in a sleep mode, thus saving battery usage until a wake-up signal requesting use of the sensor is received. Powering of the wake-up circuitry may be supplied through energy captured using an energy harvester. In one example, the energy for powering the wake-up circuitry is extracted from the same signal used for awakening the sensor. The wireless sensor mode may operate in a passive mode, in which the energy for powering the wake-up circuitry is harvested, or in a power supply-assisted mode, in which some of the power is provided by a power supply. High quality factors filters may be used to increase the signal-to-noise ratio of the wake-up signals, thus improving the node's ability to recognize activation requests.