Worn on the students’ wrist, the Practi-CRdM will provide an audible “beep” when compression depth is not within the range of 5-6 cm (2”-2.3”). A diode illuminates red when compressions are below 100 cpm or above 120 cpm. When compression rate is between 100 and 120 cpm, the diode illuminates green, allowing users to self-check their timing. Fits any size wrist and may be used with any training manikin. The rechargeable lithium battery lasts a minimum of 3-4 hours and may be charged via USB port. 1 year warranty.