How long do 123 batteries last in a smoke detector?

We've had several issues of false alarms, and each time this seems to be solved by replacing with fresh batteries. But it seems we have to do this every 4-6 months. This week, we had an alarm start chirping due to low battery, but again, it was only about 5 months old.

I know the website says 3-5 years, but is it really that in practice? I've been using Energizer brand. Any brand recommendations?

We have 9 detectors and this is becoming a large expense :P