The whole purpose is to have an alarm before my blood-alcohol level gets dangerously low. But the "battery level" suggestion gives me an idea. Basically reverse the process. An LED/sensor for each bottle. If the bottles are arranged in a line, then as each gets removed, the corresponding LED/sensor will indicate it's absense. A counter to determine the number of bottles left, and an alarm set to the minimum number. Alternatively, I could just use a summing amplifier, and a scaled input from each sensor, output to a comparator with the reference set to an appropriate level. Think we might be on to something!