I am thinking any of your Remote start/Alarm companies nowadays have the "remote" feature you are asking about, packaged into their ECU's (brain).
When you aquire the system you want, it will have an input for the door lock trigger. (either POS or Neg depending on your vehicle) Once wired correctly, when you arm or disarm, it will pop your locks and allow you to open the door without the key.
I sell CompuStar alarms with remote start if you haven't decided on a brand yet. They offer 2 way spread spectrum systems with incredible range or RF systems with decent range that will page your remote with triggers or system updates. I have the spread spectrum installed on my Manual trans Vette and have remote started in a parking garage of a mall from at least 3/4 of a mile away.
Email me if you want more info on these.
Just when you think it is right.....you hear something else...this NEVER ends!