I have noticed that the contact sensors on my northern/western facing windows trip in the late afternoon even if the window is closed. Do these sensors periodically need to be replaced as the age? The alarm install predates my ownership of the house but is about ten years old.
They may need replaced or adjusted, it depends on the sensor. Over time, especially if the original install was a bit off, wear and tear can widen the distance between the magnet and sensor, or it can be misaligned.
Temperature changes and direct sunlight may cause issues, but it’s hard to point to that with certainty.
If it is an old sensor and you notice regular issues with it, it very well could just be the sensor physically failing, so yeah I would replace it myself.
If you have any questions about it, post a photo of the sensor and we would be happy to see if there are any obvious issues.