The Privacy Box by Lucky225


                                 S2     R2
--------|---------------------- / ---\/\/\/\/--| (ring, red -)
        |                                       >
        |                                      <   r3
        |                                       >         (+)
        |                                      <----------
       <                                                  <telephone>
        >                                      -----------
       < r1                                   |          (-)
        >                                     |
        |                                     | 
        / S1                                  |
        |                                     |
       (||)led                                |
---------|------------------------------------| (tip, green, +)

r1= ~68ohm 
r2= ~470ohm
r3= ~220ohm
led= 1.7v
in use= in use light circuit
phone= phone
s1 = switch
s2 = switch

Use:

If another extension is picked up you can press S1 for privacy mode,
this will put a 68ohm resistor in parallel with the phone line to create
low voltage, about .5 volts, not enough to light the led.  When in
privacy mode it will be very hard to hear any of the parties on your
line.  The led will light when the person on the other extension hangs
up because the voltage will go to .7 volts causing the led to glow just
lightly. then you can turn S1 off to talk normally. (Hint: depending on
the resistance of your particular phone, the circuit may not work
propertly, try changing the resistance from 22-68ohms or different
voltage rated led's to troubleshoot)

S2 is a switch to turn on the "invisible box" which will make in-use
lights and telephone recording devices that record when an extension is
off-hook in-operative. (Also, resistance is variable, try changing
resistors if it doesn't work)