This is not something everyone needs or wants. But under the right circumstances (like being stalked) it can be a useful tip.
If you are concerned about being held hostage or kidnaped or otherwise detained against your will, you can establish a code phrase or phrases. The way this works is for you and your contact (wife/so/kid/partner etc.) to select a key phrase to use on the phone in case something really bad happens (kidnaping, break-in, etc.). The phrase should *sound* innocuous, like, “I’m fine. Be well .” It could be the use of a pet “name” which really isn’t one.
Now if you are *really* worried, a ‘code phrase’ that is NOT used may be a clue. In other words, if someone is holding you and telling you to read from a script, and you can’t say “I’m fine, take care of yourself” then they won’t know that you’re in trouble. If, on the other hand, your code is, you always end the conversation with “Take care of yourself” and you don’t use it, THEN the other party knows you’re in trouble.
The phrases themselves are not important. It’s what they mean that counts.