Assuming you're in North America and the flarm is a PowerFLARM, they have given prior notice. The PowerFLARM CORE manual version 3.40, June 16, 2014, page 23 says:

"Mandatory firmware update
In order to allow global changes of the FLARM system, every FLARM/PowerFLARM software has a fixed expiry date. Firmware update before the expiry date is mandatory for continued operation. The next such date is March 31, 2015. All FLARM/PowerFLARM devices will start warning about imminent expiry 60 days prior to the expiry date."

In the table of contents, it says "Mandatory firmware update........23".

I'm sure the Portable manual has a similar warning.

The flarm.com webpage has this:

"The ability to update the whole network without being limited by constraints of the past is one of the key features of FLARM and has allowed it to adapt to rapidly expanding requirements. Many parts of aircraft require scheduled maintenance; this is not a concept which is new to aviation."

It should be pointed out as well that this is not the first mandatory update - I did a search on ras and found in Feb 22, 2011 from the FLARM team:

"When is the next scheduled service update due? Since its creation
FLARM has maintained scheduled updates, initially in a one year cycle,
in 2006 a two year cycle, and last time in 2008 a three year cycle. As
the technology matures, we further extend this period to now four
years, i.e. version 5 expires on March 1, 2015. This is more
convenient for some users, but slows down the innovation cycle,
possibly delaying the use in new applications."

I look forward to the next update... but I wish there were an opportunity to test it a bit before the Pan American Gliding Championship starting a day or two later.