The thinnest transmitter, STB/ AV/ TX/03 is card type transmitter. It is merely 6mm in thickness and weight only 27g. The Credit Card style bug can be used as a normal listening device,however it has VOX function built. This function allows you to 'record only the action' when used with our auto recording unit or a voice activated recorder attached to the receiver unit. You can carry it in your chest pocket and it is also easily concealed in a pass holder.