How to notice a phone is ringing when left in a bag? I always carry my cellphone on me on vibrate, because I'm male and this works with my wardrobe. 

Many women I know carry the phone in their purse or other bag, and they often miss calls, not noticing the phone is ringing. At the same time, they don't want to have the ringer volume set very high, so that it's a nuisance to others.

How can they notice the phone is ringing, when it is not on their person, and not loud?
I could think off two possible alerting devices like:


A Bluetooth enabled watch - which when paired with the phone can display incoming call alerts and can even vibrate. Being a watch on our hand its vibrations can't go unnoticed. Casio has one; Amazon has few bracelets; Sony's LiveView are few options.
To wear a Bluetooth headset always so that the ring can be heard. If that looks like working for FBI :) there are jewel kind of BT devices like this one.