Unlock the following bonus options at the "Options" menu by performing the corresponding tasks:
OPTION - HOW TO UNLOCK Equipment Strength Upgrade - Collect all 103 illustrations for Tobin's Spirit Guide. Faster Health Recovery - Collect 50% of the illustrations for Tobin's Spirit Guide. Gozerian Rookie Outfit - Beat the game on the Gozerian difficulty. This outfit will allow you to be immune to sliming. Increased Scanning Speed - Scan 50% of the ghosts and scannable objects for Tobin's Spirit Guide. Invulnerability - Beat the game with all 103 illustrations collected and scan all 103 ghosts and scannable objects. No Equipment Overheat - Scan all 103 ghosts and scannable objects for Tobin's Spirit Guide.
In Ghostbusters HQ, there's a table upstairs with a phone. Interact with the message machine to the left of it to listen to a variety of voicemail. There is new voicemail each time you go to Ghostbusters HQ.