Audiovox 550, 700, and 750

Test Mode:

Press and hold the CLR, 3, and # keys (another source says CLR,3, and *
key), then hit the PWR key. The display will show "test".
02 [SND] exit test mode
07 [SND] activate transmitter
08 [SND] deactivate transmitter
09 [SND] XXXX [STO] - selects channel XXXX
10 [SND] X [STO] - sets attenuation (0-7)
24 [SND] shows the ESN.