If you are looking for a high invisibility FM parallel tapped telephone line transmitter, then watch this video for more details. This transmitter can be used with or without a battery. Using a 9V battery will ensure HIGH invisibility to detection devices. Using this circuit on telephone lines other than your own, or your business, is ILLEGAL. You can transmit in the 88-108mhz band, or just above/below that band to ensure others cannot listen in. The circuit only transmits when the phone is in use. Both sides of the conversation will be heard.