Abstract: An alarm system for a fishing apparatus that is an ice fishing tip-up employing a sensor alarm unit with a housing, processor, sensor, power source, and onboard wireless communications, the unit mountable to one of a base and fish strike indicating flagpole of the tip-up with the sensor configured to sense a magnet on the tip-up during operation and cause the processor to alarm when a fish strikes. The unit has a mounting arrangement with a clamp releasably attaching the unit to the flagpole for movement in unison therewith from an armed position towards a fish strike indicating position. The mounting arrangement includes a twist-lock dovetail joint used to removably mount the unit to the tip-up base. The dovetail joint removably attaches the housing to a unit base mounted to the tip-up base. The unit can have another sensor that senses motion, orientation, angle, rotation of the unit.