The present disclosure relates to a system for providing an acknowledgement output at an output transducer of a device in response to detection of a trigger signal. The system includes an input transducer, a signal processor, a main processor separate from the signal processor and an output driver. The signal processor monitors an input signal received at the signal processor from the input transducer and outputs an acknowledgement signal to the output driver if the received input signal corresponds to the trigger signal. The signal processor also outputs an interrupt signal to the main processor to cause the main processor to enter an active state. In this way an acknowledge output can rapidly be provided to a user of the system, as there is no need to wait until the main processor has entered its active state and processed the trigger signal.