What to do if Galaxy Watch is hot to touch during calls?

When you make or receive calls for an extended period of time, or when using features/apps that require more power, the device and its battery may temporarily heat up due to increased battery consumption. This is normal and should not affect your Galaxy Watch’s lifespan or performance. 

Moreover Galaxy Watch supports additional bandwidth compared with previous watch model (Gear S3), so more Frequency Shift
Circuits in device were added. Those components consume more power and can cause temporarily heat up the Galaxy Watch.

If the Galaxy Watch overheats or feels hot for a prolonged period, do not use it for a while. If the overheat continues, visit a Samsung Service Centre for further assistance.