Answer:
I must confess that I have always believed this to be true since it was relayed to me on many occasions and by many different pastors.
However, after much research I can tell you it does not say anyplace in the Bible this was the specific practice. Even early Jewish history books do not confirm this.
It may be true, but we cannot say for sure. Here is what the Bible does say…
Exodus 28:33-35 And beneath upon the hem of it thou shalt make pomegranates of blue, and of purple, and of scarlet, round about the hem thereof; and bells of gold between them round about: A golden bell and a pomegranate, a golden bell and a pomegranate, upon the hem of the robe round about. And it shall be upon Aaron to minister: and his sound shall be heard when he goeth in unto the holy place before the LORD, and when he cometh out, that he die not.
It does seem logical that one of the purposes of having the bells was to signify whether or not the high priest was alive and moving. Since only the high priest could enter the Holy of Holies once a year, no one would be able to go in and retrieve the body should the high priest be unprepared spiritually to go into this sacred place.
It seems like this myth or legend may have some basis, but for as many who believe it there are an equal number who dispute it, such as the well written article at http://www.christiananswers.net/q-eden/anklerope.html
My question would be, how DID they get the high priest out if something happened without some means to retrieve him?
Good question and I am glad we don’t have to rely on a high priest here on earth any more to do this for us. Hebrews 9:11-12 But Christ being come an high priest of good things to come, by a greater and more perfect tabernacle, not made with hands, that is to say, not of this building; Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us.