The best replacement for pedometer is heart rate monitor.

The best alternatives to pedometer are rated as following:
★★★★★  heart rate monitor
★★★  accelerometer
★★  odometer
★  fitbit

Your alternative for pedometer is not listed? Suggest!
Speaking about pedometer, one probably shouldn't forget about heart rate monitor.

Other search terms related to pedometer and their ratings are:
★★★★★ heart rate monitor
★★★★ heart monitor
★★★★ watch
★★ altimeter
You have in mind a companion for pedometer and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of pedometer in all years. Click on graph for more.
pedometer
heart rate monitor
accelerometer