How do I know which strap width fits my watch?

What matters is not the case size but the gap between the lugs, measured in millimetres — most often 18, 20 or 22 mm. Measure between the lugs with a ruler, or check the watch's specification. Apple Watch and some Samsung models use their own fitting, so they need a strap made for that model.

Does a smartwatch need its own SIM card?

Most do not. Standard models connect to the phone over Bluetooth and use its connection. A separate eSIM is only needed on LTE versions, if you want to take calls and messages with the phone left at home.

What does a watch's water resistance actually mean?

5 ATM means the watch will survive rain, washing your hands and swimming in a pool, but not diving or a hot shower — steam damages the seals. IP68 means protection against dust and brief immersion, but it is not meant for swimming. Leather straps do not survive water even when the watch does.

Smart Watch

Apple Watch Ultra 3 MF1H4ET/A – GPS + Cellular smartwatch, 49 mm Always-On Retina, black/charcoal

Name: Apple Watch Ultra 3 MF1H4ET/A – GPS + Cellular smartwatch, 49 mm Always-On Retina, black/charcoal
Brand: Apple
SKU: 6984283
Price: 1047.99 EUR
Availability: InStock