how can i fix my remote for the alarm on my vectra?

hi i have got 2 remotes for my vauxhall vectra on my car keys 1 built into my key and a separate 1. I would normally use the 1 built into the key but i thorght i would use the separate remote, well when i used that 1 the 1 built into the key would not work anymore, can u tell me what has happened and if you know how to fix it? Thanks very much