You can make a Tyristor by combining two transistors. The result is a pnpn sandwich which acts like one which is made in a single stack.
The tyristor ignites when the voltage in the capacitor is slightly greater than behind the two diodes (Ubatt - 2x0.7V) and keeps discharging until the capacitor is drained so the current stops. An LED can handle the massive current if the pulse is short enough. You can increase the size of the capacitor to slow the frequency down without harm. In this Simulation a small capacitor is better to avoid waiting for too long.
Current consumption is minimal, one old "dead" 9V battery lasts many days. Now you can make use of your old batteries too weak for smoke detectors.
