Powermeter systems pedal based
The simplest and fastest way to upgrade a bike's poermeter system is a system that is installed in the pedals. In this case strain gauges and the appropriate electronics are placed in / on the pedal axles and reliably measure the occurring forces. The electronics transmit the digital signals via Bluetooth, ANT + to your bike computer. The entry is quite cost-effective, since there are one-sided systems that absorb the force on one side and the built-in electronics calculate the missing side. If you need more accurate data, you can simply buy the missing second pedal with power measurement.
The great advantage of these power meters is the easy change for several bicycles, since you only have to screw the pedal.