If you see a blink every 4 seconds this is a general sensor fault, not a dirty sensing element. A blink every 8 seconds indicates contamination.
A general fault is typically a hardware/sensing element failure. This isn’t common, but becomes a bit more likely the longer it is installed.
To replace, you would need to program a new SMKT3 sensor into your panel, it would not listen for the new sensor unless you added it to programming.
You can find an installation video on the SMKT3 here, along with step by step programming.