Passed this video on youtube:
https://www.youtube.com/watch?v=XfNWDvl7qAo
And apparently that also works on the FR235 :)
With the watch turned off, press down and power to turn it on and keep down pressed while it's booting
Then you'll end up in the service menu where you can do some tests and see some info (nothing really useful as far as I can tell but hey, still funny).