With Pedal Assist Sensors, an electric bike automatically turns on the motor when you pedal. Pedal assist eliminates the need to use a throttle to control the motor. There are two basic types of Pedal Sensors: CADENCE which measures IF you are pedaling and TORQUE which measures HOW HARD you are pedaling.
The basic cadence sensor uses a magnet on the crank, which turns the motor ON when you pedal and off when you stop. Basically, it works like a switch. Using the cadence sensor, you can adjust the assist mode manually up and down to adjust the boost level and speed. Cadence pedal sensors are available on most basic e-bikes. It is an inexpensive way to add pedal assistance to the bicycle, but the disadvantage is that it can feel jerky, sluggish, and counterintuitive. In addition, if you pedal faster than the motor is spinning, the motor will actively work against your efforts.
The torque sensor uses a strain gauge that is a totally different technology. The pedal force is measured at 1,000 samples per second over the entire pedal stroke. To determine how much electric power to push to the bike, a torque sensor measures how hard the rider is pedaling. The harder you pedal, the more power the motor gets. The lighter you pedal, the less power the motor gets. Since the adjustment is made in real time, your every input is amplified, making you feel like a bionic! Higher-end e-bikes often use torque sensors, and cadence-only sensors are not allowed in some countries. Because the precision component is relatively more expensive, the cost of implementing this technology is significantly higher.