Built way back in the 1980s this CMOS Car Alarm provided an entry & exit alarm for my wonderful little Mini. It was built from CMOS series logic to reduce the current consumption and the circuit only drew 20mA with both LEDs lit! I particularly like the oscillator design and the fact you don’t need any current limiting on the LEDs as the CMOS logic self-limits. Enjoy!
Build something that uses or abuses a logic chip and get amazing boards, tools, and other swag. The Open 7400 Logic Competition promotes awareness of the basic building blocks of modern circuits. Devious geeks ignited the computer revolution with discrete logic computers, what can you do? Details and entry form here.