This circuit uses a LM3909 "Led Flasher" 8 pin DIP integrated circuitic as the central component. The .22 ufd capacitor sets the "Flash Rate" frequency. The output frequency using a .22 ufd cap. is approx. 600 Hz. The output level is approx -10 dBm, open circuit and -12 dBm with 600 ohm load. The output waveshape is a squarewave. With a 1.5v "D" cell this circuit will operate for more that a year. This entire circuit including the battery, battery holder, circuit and output jack can be mounted inside a 4 x 2 x 1.5 inch minibox. I have made a number of these, one for each toolbox or site and made up several different output cables, the most useful has a 1/8" plug on one end and alligator clips or telco style bend nose clips on the other.