Nissan uses a flashing key image to relay information to the driver about either the doors being unlocked or about the key itself. Fixing this issue rarely requires any maintenance at a repair shop.
A key sign on a Nissan Serena can be red or green and solid or flashing. The dashboard flashes a red key sign when the car is off and doors are unlocked and a solid red key if the car is off with the doors locked.
A flashing green key sign appears if the battery of the key needs to be replaced.
The red key sign with the ignition off informs passengers whether the doors are locked. This does not drain the battery and it's a normal function on the Nissan Serena.
The flashing green key means the battery needs replacement. The Serena's key fob has a switch that allows you to remove the metal key. Then the fob can be popped open with a small flathead screwdriver. The old battery will be labelled with its type, which is likely C+.
A dealer or repair shop can diagnose other issues if a Serena has an unexplained flashing key sign. If a red key flashes with the doors locked, there could be an obstruction inside a door. If a flashing green key persists, there may be an issue with the ignition's key sensor.