Six standard detectors are available. Product\r\nnumber 4244, 4344 and 4444 are our\r\nstandard models. Numbers 4544, 4644 and\r\n4744 feature a self test function. \r\n\r\nSelf test models have a continuous flashing light and\r\nbeep to indicate that the batteries are charged\r\nand the unit is functioning properly including\r\nthe detection circuit and the light and\r\nbuzzer.\r\n\r\nIt is good practice to test the detector prior each use in order to make sure that the unit is working properly.\r\n\r\nYou can purchase our Voltage Detector Tester part #4445 for the testing of the standard models.