Swatch

From 2006.igem.org

The idea is to develop a relative fast and mainly robust and precise (otherwise it wouldn't be a swiss watch ;-)) triggering of at least 2 different output signals in order to distinguish between minutes and hours (as the processes are not so fast it would be more likely hours and days).

As bacterias duplicate rather fast and in regular intervals - as long as the environment alows it - one could try to use this process for triggering.