I have conducted a few weddings that have used a Ring Warming in their ceremony. It is a great way to get all of your guests involved. It is especially beautiful when you have a smallish wedding, not something that I would generally recommend for a very large wedding. A Ring Warming usually happens around the beginning of the ceremony as it takes a little bit of time. What happens is the wedding rings are passed around the guests, either in a small bag or box, or sometimes tied to a small ring cushion. All of the people present are asked to hold the rings and say a silent prayer, make a wish or silent blessing for your marriage. I have also heard of larger weddings where the rings are only warmed by the wedding party and the close relatives, which is an option, but I personally think it is a lovely way to make everyone that is present on your special day feel a part of it all.
I wonder, however, if people worry about their rings being passed around to all of their guests? Not that they think anyone would steal them, but more worried about people getting distracted by other parts of the ceremony or possibly dropping them, which could create some problems depending on where the ceremony is being held.
A great way to elevate any fears about this is to have someone look after them as they are being passed around. It is a great job for someone who is special to you that you were not able to have in the bridal party, or one of your relatives that you wanted to have contribute to your ceremony. It is a great job if you have a ring barer that is a little bit older, as they can be trusted and usually take the role quite seriously but can help if they are at an age where some of the ceremony might bore them.