First, make your retinal scanner brush, and turn it into a func_wall. Name it "fw_retscan".
Next, place a big trigger_once area around the retinal scanner. Go into its properties and let it target "ss_sci_retscan". Now go into its Flags and check Monsters and No Clients. This will only allow monsters but not the player to trigger the once.
Next, place an scripted_sequence in front of the retinal scanner. Name it "ss_sci_retscan". Let it target "mm_retscan". Type in "sci_retscan" in the Target Monster property. Type in the retinal scanning animation in the Action Animation field. Finally, set Move to Position to Walk.
Now place a monster_scientist, and name it "sci_retscan".
Next, place a multimanager. Name it "mm_retscan". Open up its properties and turn off SmartEdit. Add the following keyvalues:
Key: fw_retscan
Value: 3
Key: (the name of the door you wish to open)
Value: 5
You may have to experiment with the values (these are basically delay before trigger properties (in seconds)) to get the entire sequence to look good. You may also add an ambient_generic for bleeping sounds when the retinal scanner is uhm... scanning. Just be sure to add the triggers for the sounds to the multimanager.
If it doesn't work, ill make you an example map of the above example.