the shield is a big and blue and envelopes your ship, and when it gets knocked off you get a loud klaxon and a flashing red bit on the screen where a previously full bar annotated as "shield" is now an entirely empty bar. At which point the shield is flashing for about 2 seconds, giving you as many seconds worth of invulnerability until you can be killed.
Not sure I could warn the player anymore
![Grin](images/smilies/d_grin.gif)