Can be set to either a 2 or 3 minute round length with the flip of a switch. Can be used with AC or DC power. Plug into electrical outlet - or run on 4 "C" batteries you provide. 30-second end-of-round warning whistle lets you know exactly how much time is left - finish the end of each round strong. Timer is designed with a 5 second delay when initially started to allow time to get ready before beginning bell rings. Easy ON/OFF switch - can be reset anytime. Complete 1-year warranty.