Peugeot 208 reverse sounder not working

Could put car in reverse with ignition on and listen to each rear sensor or put your finger on sensors and see if you can feel a slight buzzing to see if they are operating .Otherwise you need to scan it with Peugeot Planet diagnostics or similar Some cars had the option of switching it off and occasionally this would happen accidently but varies from car to car and would show if available in owners h/ book .

sensors working as picture comes up on screen with white orange and red bars just no sound even radio volume lowers

Go into your settings menu screen , scroll through and see if any have been accidently muted or need resetting .On other cars this can be adjusted / set , but not sure on your car .

Does anyone know where sounder is located ?

Could be in the boot along with the sensor module .

Do you know where about in the boot as it seems if I slam boot shut starts to work again

Cant really help with that car but on other makes it was often fitted up near the parcel shelf location