The 2pk Rod Tip Bite Indicators is supplied with two attachment clamps, 3mm and 5mm to fit different rod tip diameters. The strike alert clamps securely to the rod tip. Shows a steady blue light when on standby, and flashes red when a fish bites. Visible from up to 100 yards. Water resistant, so can be used in the rain. Automatically activated when attached to the rod tip section. Power requirement 1 x CR1225/3v battery (included). Two per pack.Water resistant.3mm and 5mm.Battery included.