This step is incredibly difficult. I finally got the sensor snapped into place (gently), but could not get the clip in. Worst part was I placed the battery too close to the sensor chassis. So I think this is why I could not “slide” the clip into place. In the end, I left the clip off and put the phone back together. Everything works as before.

Do you recall the 1 TB Time Machine?  I thought that thing was built solid, but it lasted exactly one day past the warranty expiration date.  Failed due to a massive design flaw (no fan).  With that much power going to drive the huge magnet on that speaker, I doubt it will last.  The epoxy will solidify with no way for the heat to escape, then break apart after repeated use of playing music.  You may say air will flow through with the movement of the cone, but I don’t think it will be static enough to properly cool over repeated use.  That thing will break one day after the warranty expires.

Followed instructions and had a perfect installation. Two tips: before unscrewing the battery clips, pry up the battery to loosen it from the adhesive, carefully. Then unscrew the clip and carefully pry it up. That way, there's no frantic popping of the grounding clip. Then pull off the battery. Also, once put back together, power up, then remove the SIM card and reinstall (like everyone else is doing). Presto, new battery and fully functioning iPhone 4s.