Phone-In-Use Indicator

Circuit to illuminate an LED when any phone extention is off-the-hook,
LED should illuminate when circuit is not connected to the phone line,
or when the phone is off-the-hook.  If the LED fails to extinguish,
check for 3 to 4 volts across the 680 Kê resistor and check the
polarity of connections to the phone line.

                                                +3 Volt Battery
                                                 ^
                                                 |
Phone line  (+) <----\/\/\/----+-----+-----------+------------------+
                     R1        |  R3 \                            R4|
                            C1-+-    /                              \
                              -+-    \                              /
                               |     /                              \
Phone line  (-) <----\/\/\/----+-----+                              /
                     R2              |                              |
                                     |                       ....../
                                     |                    T1.   |< .
                                     |          +---------------´  .
                                     |          |           .   |\ .
                                     |   ....../              .....\
                                     |T2.   |/ .                    |
Parts List:                          +------´  .                 LED
R1   3.3 Mê                             .   |\ .                    Â
R2   3.3 Mê                               .....>                    |
R3   680 Kê                                     |                   |
R4   100 ê                                      +----+--------------+
C1   .01 æF                                          |
T1   2N3906                                         -_-  Battery (-)
T2   2N3904                                          .