My girlfriend has an insulin pump made by Medco. It has to do certain things like, if she has a certain high blood sugar level, give the right amount of insulin dose for the next hour to bring her into a normal range. If she eats, she estimates the amount of carbs she's eaten, enters in a certain dose level, and the pump calculates how much insulin she needs, based on the type of insulin she's using.
It uses a AAA battery. If the battery starts to run low, it beeps. If the battery is almost dead it beeps A LOT to let her know to change batteries.
Now... if she gets low on insulin, it will beep once or twice at approximately 10% left, and a few times at 5% left.
IF the pump runs out of insulin---THE PUMP SAYS NOTHING. No "OMG! NO INSULIN!" messages. NO WILD BEEPING! Nothing! If she somehow runs out of insulin in her sleep, she is well and truly fucked as the pump isn't going to wake her up! Nice of it to let her know when the battery is low (obviously if the battery is dead, it can't beep right?), but not so nice of it NOT to let her know when she's actually out of the life-giving fluid she needs to live.
Has it happened that she's run out of insulin and not noticed because the pump didn't say anything? Yes, it has. Luckily not when she's been asleep, but it could happen.
Good thing she doesn't have to milk a hairless cat to live, huh? Still, a little better design here might make a difference.