-- he tells you Savannah sent you a package, which you'll find on the second floor landing. The stuff inside is ... odd.
What you have here is a note from Savannah, an EMF sensor, and a book of interviews with locals about ghost sightings on this island.
You may remember the EMF sensor from previous ND games. It's a device that detects electromagnetic fields (hence the abbreviation EMF), and some people think they show evidence of ghostly activity -- though personally I have my doubts.
As for its use in this game, it's mostly irrelevant. You can pull it out to check for the presence of an electrical field any time you want, but the readings seem to be random.
The one time you really need to use the EMF detector is when you're trying to follow the first "weird note."