Apple’s widening effort to turn its nine-year-old watch from a luxury timepiece into the ultimate all-in-one medical device is taking it into territory that is legally treacherous as well as potentially profitable.

This month’s suspension of Apple Watch sales was the starkest sign yet that the world’s most valuable tech company is treading new ground as it adds health features to the device. While Apple on Wednesday won a temporary reprieve to resume sales, specialists in medical devices say the technical and legal challenges are likely to continue.