An apparatus (100) comprises a wireless sensor system (102) with electronic circuitry (104) and a power supply (106) for powering the electronic circuitry. The power supply comprises a primary cell (108) and an energy scavenger (110). The energy scavenger scavenges ambient energy and converts the scavenged ambient energy into electric energy. The sensor system is configured for having the primary cell power the electronic circuitry when the energy scavenger is inactive. The system is configured for performing at least one of having the energy scavenger power the electronic circuitry via the primary cell when the energy scavenger is active, using a capacitance of the primary cell as a buffer for the electric energy; and having the energy scavenger recharge the primary cell.