https://www.righto.com/2021/01/reverse-engineering-low-power-led.html?showComment=1610555752880&m=0
How do you make an LED blink? A vintage way is the LM3909, a chip from 1975 that can flash an LED for a year from a single flashlight batt...
reverse engineeringlow powerled flasherchip
https://makezine.com/article/technology/two-transistor-led-flashe/
Tony writes - "This circuit will flash a bright or high-brightness red LED (5000+ mcd). Good for fake car alarm or other attention getting device.
led flashertwotransistormake