Indispensable for carp fishing day and night, the 
detectors  are mainly purchased in detector central set boxes. This is very practical as in one purchase you have the number of bite detectors you need (2, 3 or 4) and the appropriate central unit, and possibly a storage box. The connection between the central unit and the detectors is wireless, the distance can vary depending on the transmission power and any obstacles or the slope between the 2 elements. Thus you will be certain to have a complete equipment to detect bites at a distance, provided that you add some 
squirrels  (hanger or swinger) to complete, or even other 
accessories  such as snag bars for example. The best known brands for their bite detector kits are 
Delkim, 
JRC, 
Carp Spirit, 
Nash  with its Siren range and of course the 
Fox  brand with its Micron.