TechJoint posted about some of the coolest and most innovative inventions out there. Here are some pretty clever invention you can buy on Amazon for under $30. Playbulb Candle cost $18.97. Hydaway Bottle cost $14.95. Kinsa Smart Thermometer cost $14.46. Pocket Tripod cost $25. Mynt Smart Tracker cost $19.99. Watch the video below to learn more about the products.