Keypad Schematic

Spy Gadgets?

This is kinda of weird, but I was wondering if anyone knows a good website that I can get Schematics/circuit diagrams (same thing) for types of electronic devices that are popularly called “spy gadgets”? Things such as Micro FM Transmitters, Voice Changers, etc. Also something like a keypad lock would be appreciated.

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10 Buttons PIC Touch-Pad with BCD Output