The best replacement for accelerometer is gyroscope.

The best alternatives to accelerometer are rated as following:
★★★★★  gyroscope
★★★  pedometer
★★  gyroscope iphone
★★  gyroscope android
★★  inclinometer
★★  velometer
★  g-sensor
★  gyro
★  core motion
★  g sensor
★  gyro sensor
★  gravity sensor
★  lvdt
★  geophone
★  imu
★  velocity transducer
★  gyrometer
★  linear acceleration
★  tilt sensor
  heart rate monitor
  magnetometer
  strain gage
  velocimeter

Your alternative for accelerometer is not listed? Suggest!
Speaking about accelerometer, one probably shouldn't forget about gyroscope.

Other search terms related to accelerometer and their ratings are:
★★★★★ gyroscope
★★★★ microcontroller
You have in mind a companion for accelerometer and it is not yet here? Propose!



Google Trends

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