For those with a Real Care 2 BTIO, if you don't want to wear the ID, try this trick I discovered for myself!
Go to a local craft store and go to the jewelry section. Buy some pins that you'd glue to the back of a handmade broach.
Use crazy glue or hot glue to glue it to the back of the ID. Once the glue dries, pin it to the tag inside the baby's pants or if they are wearing a sleeper, pin it in there close to the butt area. Now when you're baby starts to cry it should automatically chime. If it does not, pick up your baby and it should.
I have a few photos to demonstrate. The last photo shows the slight bump that appears from the pin underneath the clothes...but because it's in the pants it's very discreet.
Also, remember that with a RealCare 2 the ID can be touched to the front or the back and the speaker is in the front. Put the baby in a onesie with a cloth under it covering the speaker so the crying won't be too loud and you can also put the ID with it and it works great.