I've spent nearly 300 nights in hotels and Airbnbs over the past year, and there's a small detail I check to see how clean a room is

A year ago, I left New York to travel around the world as Business Insider's international correspondent. Over that time, I've visited over 20 countries, taken dozens of flights, and stayed in nearly 100 hotels.I am constantly staying in hotels that run the range from ultra-budget to mid-tier to luxury. Depending on the country and the hotel company, those categories could mean very different things in terms of amenities, quality, and cleanliness.Every time I enter a hotel room or an Airbnb, I check the electric kettle or coffee maker — a standard item in nearly every hotel room — to see how clean it is. Poorly maintained or sloppily cleaned hotels will often have dirty, rusted, or outright moldy electric kettles.Travel long enough and you develop strange habits.Hotel rooms are notoriously unclean places. One recent study found that 81% of hotel surfaces sampled contained at least some amount of fecal bacteria. I'm by no means a germaphobe, but I do avoid certain parts of a hotel room. I say goodbye to the throw pillows, forget about sitting on the armchair or ottoman, wipe down the TV remote, and walk around in socks or flip-flops.As I've traveled over the past year, I've experienced hotels and Airbnbs with varying standards of upkeep, maintenance, and cleanliness, regardless of how many stars it has; a five-star hotel in one country does not necessarily mean the same thing as a five-star hotel in another.But over those nearly 300 nights I've spent in hotels and Airbnbs, I have found that consistently the best barometer of cleanliness is the coffeemaker or electric kettle. Almost every hotel room has one and it can tell you a lot about how detail-oriented the housekeeping is.Because coffeemakers and electric kettles constantly have water or moisture in them, they can be a haven for bacteria, rust, and mold. If they aren't cleaned regularly — and I mean with vinegar, not rinsed with hot water — they quickly become gross. As such a small item and a tedious one to clean, I've found that coffeemakers and electric kettles are frequently overlooked by less diligent hotels.Even if the kettle is cleaned regularly, with frequent use, some amount of rust is unavoidable. But that's frequently a signal that a room or rental needs some sprucing up. When I get to a new hotel room, I pop open the top to the appliance. If I see mold or rust, which happens often, I ask for a new room or shorten my stay to one night and move on to a different place.If they're leaving a rusted kettle in the room, it's a signal to me that no one is keeping a close eye on the room's long-term upkeep. If there's mold in the coffeemaker or kettle, what else hasn't gotten a thorough cleaning？More tips from Business Insider's international correspondent:I switched to Android after more than a decade with the iPhone, and I'm not going back. Here's why.I use the same trick in any city I visit to make sure I find amazing foodCouchsurfing has a hidden feature that helped me have the wildest night in Tokyo partying until sunriseI found out the hard way that one of the best strategies to save money on flights can end up costing you big timeThe single best piece of advice I can give you for any trip you takeI've traveled to more than 30 countries, and here are the dumbest mistakes I made on the road that I'll never make agai