More than 1.5 million people are projected to flock to Philly to be in the vicinity of Pope Francis — and they all need somewhere to crash. With so many Philadelphians using services like Airbnb to rent out their houses and apartments (or single rooms) for the papal weekend, we asked a security expert what to keep in mind before handing over your spare keys to a stranger and fleeing the city.

Related: Feds: Philadelphia a no-drone zone when Pope Francis comes to town 

“I would recommend some kind of remote monitoring — some way to keep an eye on things,” says Todd Morris, head of New York-based Brickhouse Security. The company sells the MORzA BnB security system, designed specifically for Airbnb hosts with door and window sensors, a keypad-operated lock and a touch-screen control panel that lets you keep track of any “telltale signs that there’s a party or there’s a problem,” Morris says. 

Related: What to buy: fun things in the Pope store

For example, he explains, if you have a door sensor you can see if the door is opening a suspicious number of times in a short period (is your renter throwing a wild party?) or being left ajar for hours. 

Here are a few more tips on protecting your home before, during and after you rent it out. 

DO YOUR HOMEWORK

When you’re evaluating who to let stay in your apartment through Airbnb, look into a user’s past: The site lets people who’ve rented out before post reviews and give ratings. 

 “One of the big advantages of Airbnb is seeing the people’s history,” Morris says. “If someone has a long history with Airbnb, I would go with them instead of a shorter list.”

 And rest assured that Airbnb pays attention to who’s using the site: “We have a verified ID system, so we actually link a government-issued ID like a driver’s license or passport, and social media accounts, so you know this is going to be a real person,” says Alex Ward, head of new markets in the U.S. for Airbnb.

COMMUNICATE, EMOJIS OPTIONAL

“With the World Meeting of Families and the Democratic National Convention, there’s never been a better time to become a host in Philadelphia,” Ward says. 

Once you’ve signed up on the site, listed your home, vetted renters and narrowed down the lucky future houseguest, “use the two-way messaging system [on Airbnb.com] that’s safe and secure,” Ward says. “It’s as easy as texting. Find out why they’re excited about your listing and make sure they’re a good fit for you.”

WRITE DOWN THE RULES

Lay down the law, in a friendly way. “Create a little welcome packet,” suggests Morris. “The welcome packet should be part hospitality, part setting guidelines. Create a document that says ‘Here’s some fun stuff in the neighborhood, and here’s the house rules — we’ll be keeping an eye on things remotely.’ If you don’t want them to have more than three guests in the house, let them know up front.”

THROW AWAY THE KEYS

Once your guests leave, change the locks. You never know if someone has copied your keys. Or, suggests Morris, “have one deadbolt that only you have keys to.”