We already have a solution for that- does anyone remember the 'Skylab early warning helmet'? It was on SNL and had a plastic spire on top with notches indicating the remaining time the wearer had to leave the immediate area. If memory serves, the numbers were nanoseconds and really, it was pretty funny.
Fortunately Skylab ended up dropping over (into) Australia. Which probably started the Aussies shooting at the thing on the way down, sparking the current draconian gun control in that country. Opps, wrong thread....
Brian