Your key fob works perfectly until the moment you're in a hurry — and then nothing. Before you panic or order an expensive replacement, work through these troubleshooting steps. Most fob failures have a simple fix.
The overwhelming majority of key fob failures are simply a dead battery. Most fobs use a CR2032 coin battery available at any pharmacy or electronics store for under $3. Use a small flathead screwdriver to pry the fob casing open at the seam, note the battery orientation, and swap it out. Test immediately.
All key fobs have a hidden metal key blade inside (look for a release slider or button). If the fob doesn't work electronically, the blade gets you in. Once in the car, the transponder chip in the fob head should still start the car by holding it near the start button or ignition.
Electronic key fobs operate on radio frequencies that can be temporarily blocked by: large metal structures (parking garages), strong radio interference sources, some aftermarket alarms. Move to a different location and try again. If the fob works in a different spot, interference was the culprit.
Sometimes the fob loses sync with the car's receiver — especially after a battery replacement or dead car battery. Each manufacturer has a specific resync procedure (usually involving getting in and out of the car, pressing lock/unlock sequences). Check your owner's manual or search '[your car model] key fob resync procedure.'
Drops, water exposure, and extreme temperatures can damage the fob's internal circuit board. Open the fob and inspect the circuit board for corrosion (green discoloration) or broken contacts. Corrosion can sometimes be cleaned with isopropyl alcohol and a soft brush.
If the above steps don't resolve the issue, the fob may need reprogramming or replacement. An automotive locksmith can diagnose whether it's a fob or receiver issue, program a replacement fob on-site, and often do so significantly cheaper than a dealership.