Smith & Wesson has issued a recall on their popular M&P Shield pistols made before August 19, 2013. They have identified a condition whereby the trigger bar pin could damage the lower trigger in such a way as to cause the drop safety feature not to work. If a pistol with this condition were to be dropped, it could fire unintentionally. While S&W thinks this condition may only be present in some more recently manufactured Shields, they are being cautious.
To help determine if your M&P Shield is one of the pistols with this defect, Smith & Wesson has released a YouTube video showing exactly how to determine if the trigger bar bin is not functioning correctly.
Kudos to S& W for not only issuing the recall but posting this video showing owners on how to inspect their pistol for this potential defect. If a picture is worth a 1,000 words, then a video ups that by a factor of 10.