A small badge, with a microcontroller, accelerometer, 3V lithium battery, 10 LEDs and one button. When you press it, it shows how active you were during past 7 hours, an during last 7 days. That's all. If you were too inactive for a couple of hours, it blinks and warns you that it's time for a walk. To do it correctly, it detects and ignores periods when the badge is stationary.
The low-power accelerometer LIS3 monitors your activity and PIC18F23K20 periodically wakes up and collects data.