You can already use augmented reality apps on your smartphone to measure things. The Arrim ONE takes it to the next level. It lets you measure straight lines, circles, angles, and circles. The device only has a button for power on/off. The rest is handled on your phone.
Arrim ONE is accurate to +/- 1.5 mm within 20 meters range. It measures only 5cm long and 3cm wide, weighing only 35 grams. The battery lasts for 1000 measurements.