Final countdown clock
This is definitely one of the most suspensful artifacts. When this artifact is made by a tinker, it plays once a day for five weeks. After that, it plays once every twelve hours for five days. Then once every hour for three days, once every ten minutes for one day, then once every five minutes for half a day. After that, it plays once more before it explodes. The hero can't reset this device, so in order to get rid of it the hero must sell the final countdown clock. There is no way to tell what stage it is in until it goes off, and the hero recognizes the pattern.