You don't have to ditch your favorite wristwatch to get in on the smartwatch trend, said Nathan Olivarez-Giles at The Wall Street Journal. Chronos, "a slim, stainless steel disk that sticks to the underside of any watch," can turn just about any old-fashioned timepiece into a basic smartwatch, complete with phone notifications and fitness tracking.

The Chronos disc, which is small and thin enough to fit about 80 percent of watches on the market, glows or vibrates to alert wearers to phone calls, text messages, and app notifications on their smartphones. Different light and vibration patterns can be programmed for different alerts — say, "purple for an Uber ride arriving." It also can track steps and distance traveled. Chronos is available now for pre-order at $99, rising to $129 once it ships in spring 2016.