An apparatus comprising: electronic circuitry with a signal processing system for executing a plurality of pre-determined signal processing tasks; and an energy source configured for powering the electronic circuitry in operational use of the apparatus, the energy source is operative to supply an amount of energy that varies over a service life of the energy source, the energy source comprises: an energy scavenger for scavenging ambient energy; and an energy storage configured for storing the ambient energy scavenged by the energy scavenger; wherein: the electronic circuitry comprises an energy control component; the energy control component is operative to connect the energy source and the signal processing system if a first magnitude of the amount is higher than a first pre-determined threshold, and to disconnect the energy source and the signal processing system if a second magnitude of the amount is lower than a second pre-determined threshold; the first pre-determined threshold is higher than the second pre-determined threshold; and the electronic circuitry is configured for: determining the amount of energy available from the energy source; and selecting for execution a specific one of the plurality of pre-determined signal processing tasks in dependence on the amount determined. electronic circuitry with a signal processing system for executing a plurality of pre-determined signal processing tasks; and an energy source configured for powering the electronic circuitry in operational use of the apparatus, the energy source is operative to supply an amount of energy that varies over a service life of the energy source, the energy source comprises: an energy scavenger for scavenging ambient energy; and an energy storage configured for storing the ambient energy scavenged by the energy scavenger; wherein: the electronic circuitry comprises an energy control component; the energy control component is operative to connect the energy source and the signal processing system if a first magnitude of the amount is higher than a first pre-determined threshold, and to disconnect the energy source and the signal processing system if a second magnitude of the amount is lower than a second pre-determined threshold; the first pre-determined threshold is higher than the second pre-determined threshold; and the electronic circuitry is configured for: determining the amount of energy available from the energy source; and selecting for execution a specific one of the plurality of pre-determined signal processing tasks in dependence on the amount determined. an energy scavenger for scavenging ambient energy; and an energy storage configured for storing the ambient energy scavenged by the energy scavenger; the electronic circuitry comprises an energy control component; the energy control component is operative to connect the energy source and the signal processing system if a first magnitude of the amount is higher than a first pre-determined threshold, and to disconnect the energy source and the signal processing system if a second magnitude of the amount is lower than a second pre-determined threshold; the first pre-determined threshold is higher than the second pre-determined threshold; and the electronic circuitry is configured for: determining the amount of energy available from the energy source; and selecting for execution a specific one of the plurality of pre-determined signal processing tasks in dependence on the amount determined. determining the amount of energy available from the energy source; and selecting for execution a specific one of the plurality of pre-determined signal processing tasks in dependence on the amount determined.