Undetectable on phone line. Needs no battery, operates on phone line power! Easily connected to any tape recorder that has remote and mic jacks. Excellent audio fidelity quality. Keep a record of all your telephone calls - automatically. The tt-1 connects anywhere on the phone line and will control any standard battery powered tape recorder. The recorder automatically starts and stops whenever the phone is used and records both sides of the conversation with excellent fidelity. Super easy one hour assembly and a manual that tells you not only how to build the kit, but how it works as well. Add our matching case set for a pro look. Optional case size: 5 w x 1 1/2 h x 5 1/4 d.