The car went in for its first service recently and I asked them to investigate the key light randomly coming on.
Despite having replaced both key fob batteries the dealer claimed my key fob battery was "weak" and needed replacing.
I paid the exorbitant Nissan battery price and replaced the battery in the presence of the Service guy.
Two days later the light came back on and has continued to do it since.
It has since been back in and they reprogrammed both key fobs and they now claim they have been in touch with Nissan and the only other cause is driving with my foot resting on the clutch pedal
However, if it continues I should get back in touch.
To keep it in perspective I have made notes on my phone and the light came on after first service at:
3560 miles
3579 miles
3619 miles
3656 miles
3686 miles
The car came back yesterday when they reprogrammed the key fobs so I hope the light stays off.