1. have you really inserted the SIM card correctly? I had to push mine in hard. Make sure it is inserted the right way round (chip facing up).
2. try another SIM, if it works, it's sim.de, otherwise it's probably the watch.
3. make sure that your sim.de subscription supports roaming if you are using the watch in Switzerland. According to the manual, the watch supports roaming. (see tcl.com)

Hi, at Sunrise we had to take out a "Watch" subscription for this watch, at 10.00 per month.