There are many types of bite indicator and bite alarm, but one will be just right for the type of fishing you do. The best known are quivertips, which fit onto the end of the rod, then there are different types of 'hanger' indicators that hang between the butt ring and reel.
Electronic bite alarms can be very simple devices that do no more than indicate when the line moves over a roller and have just an on/off switch. The most complicated have volume, tone and sensitivity controls. Before buying, ask yourself what you really need, and then choose accordingly.
