Proximity sensor problem -- direct contact with fabric confuses it

Question

On the Twom (and I'd guess the Onem), if the prox. sensor is covered and the phone is locked, it disables all of the phone's buttons until the prox. sensor is uncovered. This is a good thing, because it means the volume can't accidentally be changed in your pocket so long as the phone was locked before it went in your pocket.
Here's my problem: at any small distance, the prox. sensor works exactly as it should, whether facing skin, fabric, whatever. However, if the phone is brought into direct contact with certain fabrics (like denim on my jeans), the prox sensor fails to "see" this and all the buttons remain active. This means that in my pocket, where the phone is fully in contact with the fabric, it usually still lets the ringer volume change and the phone unlock.
Anyone else notice this behavior with their phone, or is it just mine?

Answer 1

you got it right. The sensor sends out a signal, a light, that you can see if you push any of the buttons with the phone locked in low light. My guess as to how it works is it sends out a low-frequency signal, perhaps infared/borderline red light, and if it is reflected back, it recognizes it as being 'covered'. Because it is low-frequency/low-power, it only will recieve the signal back from very short distances. True, most fabric won't block it. If you're wearing tight jeans/pants, then it does work if you put hte screen-side against your leg. But what i did was file down the volume keys anyways. They sit about half as high as they were originally, and now it is very hard for them to be accidentally changed, but they still can be pushed for the camera zoom, or volume change, when i want.