Peugeot 206 (2002) ?

you dont say if it has drum or disc brakes. if drum brakes you need to remove drum to inspect brakes to identify fault. if it disc brakes you can usually see through wheel if brake pads are very low. may just need pads or may have damaged discs.
you need to remove airbag from steering wheel to re route wires to your horn push. one will be touching an earth and will be making horn go off randomly.

me
April 2009