Japan’s NTT DoCoMo Inc has unveiled a new fitness phone prototype that has a sensor to keep track of your physical activity each day and let’s you know how many calories you’ve burned.

The phone, unveiled this week at the CEATEC electronics show outside Tokyo, has an inbuilt motion sensor that detects body movement and calculates how many calories you burn.

The sensor can tell whether you’re walking, running, climbing stairs, or resting, and counts the calories accordingly to tally daily totals, Tobita said.

“It’s with you wherever you go, like a portable personal trainer,” he said.

NTT DoCoMo doesn’t sell their phones outside of the Japanese market, but expect the technology to arrive elsewhere in the coming months.