In order to allow global and synchronized changes to the FLARM ecosystem, every FLARM device needs to be updated with the latest firmware version at least once per year (every 12 months). The annual firmware update must be part of the Aircraft Maintenance Program (AMP). The entry in the AMP is to be made during installation. See EASA Minor Change documents for details.
If the annual firmware update is not applied, the device may no longer be interoperable with other FLARM devices without any notification or warning.
Firmware expiry is a "last warning" implying that the AMP has not been followed. It has also been implemented to avoid that devices which have not been updated are broadcasting obsolete data. 1 month before the firmware expiration date, the system will issue a "soft warning" for 30 seconds, after which it will continue to operate normally. After the expiration date, the system will issue a continuous hard warning and will not operate.
The firmware expiration date is not related to the aircraft specific update cycle/date. The firmware will not expire as long as the firmware is kept up-to-date according to the AMP. The expiry is always at least 12 months plus a few months of margin in the future when downloaded from flarm.com.
If the annual update cycle has expired but the firmware has not yet expired, the device will in most cases continue to work until firmware expiry.