Pebbles are quite cheap and offer 7 days of battery. The company went bankrupt, but you can still use the devices with rebble. The Pebble 1 is about 40€ and the

Pebbles are quite cheap and offer 7 days of battery. The company went bankrupt, but you can still use the devices with rebble. The Pebble 1 is about 40€ and the rare Pebble 2 about 120€.