Electronics assemblies with wireless capabilities for use in a drug delivery device. At least one of the electronics assemblies includes a processor, a sensor arranged to measure a fill level of a drug container and output a measurement to the processor, a wireless module to which an external device can be paired, a power module arranged to supply power to the assembly, and memory storing instructions for the processor to perform. The instructions include activating the sensor at a first time interval and receiving the measurement signal, for each activating of the sensor at the first time internal, determining, based on the received measurement signal, a change in the fill level of the drug container, and when the change in the fill level is detected, activating the wireless module for a first duration to enable the external device to pair with the wireless module.