Japanese companies StrapyaNext and Tokyo Coil Engineering claim they developed the world’s first battery charger for cell phones based on solar energy. The charger comes in the form of a phone strap.

The device is 12.5 cm long and weighs 40 grams. It takes between 6 and 10 hours for a full charge with which you can talk for up to 40 minutes. StrapyaNext promises on the product page: “As long as the sun pours light and heat on the earth!” An AC adapter can get the job done in 3 hours.

The charger is available for $19 but for the time being, only Japanese cell phones are supported.