Conversation so far:
when do tire pressure sensors need to be replaced
On average, a TPMS sensor's battery should last between 5-7 years.
what does the TPMS do?
The TPMS warns you that your tire pressure is too low.
what tire pressure is considered too low?
Dangerously low tire pressure is 25 percent below the recommended air pressure, according to federal government regulations.

Question: how much does a sensor cost to replace?
Self-contained rewrite: how much does a tire sensor cost to replace?