For warning applications, a high brightness (IC controlled) flashing LED that flashes like an emergency vehicle strobe.
A chain of multiple rapid flashes , a pause then another chain would alert users to danger better than conventional flashing LEDs.-- FloridaManatee, Jun 03 2004 Interesting - a specific sequence of flashes which people would come to learn means 'danger'-- hippo, Jun 03 2024 random, halfbakery