This circuit can use a pendulum sensor. We found this configuration in a 1994 publication. The components used are common and the timing is given by the capacitor C1 which can be changed.
The transistors are 2N918, 2N3464 and other RF equivalents of the time for Q1. For Q2, 2N3399, 2N2894...
This circuit, which can be used as a shield, was found in a 90s Electronic Design. The circuit...
This interesting intercom circuit was obtained from an Argentine publication from the 1970s....