You can use them to make and receive calls, get notifications, take pictures, check your heart rate, and get the temperature. Of course, it will also give you the time of day.
Amazon (AMZN) has a whole new department, the Wearable Technology Electronics. Check it out. They also sell the Fitbit Flex Wireless Activity + Sleep Wristband, and even wearable cameras such as the GoPro HERO3+.
If you are looking for a great Father's Day gift (or a gift for yourself), check out the wearable technology products.