A moment of clarity

One of the smoke detectors was chirping constantly, drives me insane.
It usually means that the battery is low. I was told it's good practice to replace them all at the same time. 
Off I went to the supermarket for a replacement.  Holy shit! those 9v batteries are $6 each! There's 5 of them, that's $30 !
(Why is it that you have every battery known to man EXCEPT the one you need right now.)
Out came my phone, Amazon.ca. 
20 count, for $28, smoke detector 9v batteries including same day delivery.!
Done deal.

I need  more clarity in my life.


Ah well...