simple 4060 IC oscillator/timer which is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state, time can easily be set from seconds to hours
http://www.imagineeringezine.com/PDF-FILES/watchdog.pdf
draws only 200 nanoamps from a 1.5v supply.
http://www.imagineeringezine.com/PDF-FILES/astable.pdf
from TCJ article.
http://margo.student.utwente.nl/el/analog/cmosrcs.gif
http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#delay10.gif
30 minutes operation. Blinking LED signals 6 last minutes before turn-off.
http://space.tin.it/scienza/fladelle/Page4.htm
to control a film exposure shutter for a darkroom. It has 8 time steps ranging from 0.35 to 4 seconds. Activated by a foot switch.
http://www.imagineeringezine.com/PDF-FILES/camera.pdf
http://www.discovercircuits.com/PDF-FILES/watchdog.pdf
http://www.interq.or.jp/japan/se-inoue/e_pic6_3.htm