How Do Automatic Doors Know You're There?

0:00How do automatic doors know you're there? Hi, welcome to Curious Kids Every Day. I'm Josh. How are you doing today? It's so good to hear from you. Hey, have you ever gone to the grocery store and notice those big sliding doors that open just at the exact moment when you're ready to walk into the store? You don't even have to slow down really. You just walk right through and you trust that it's going to open just at the right time. After so many years of doing that, I don't even think about it anymore. But I can tell that my kids still get really excited going through automatic doors. It feels a little bit like magic.

1:01You just walk in front of a door and the door says, you can pass. Well, it doesn't actually say that, but that's what it feels like. Do you want to figure out how this all works today? Let's figure out how automatic doors know you're there. Automatic doors know you're there because they are constantly checking for clues that something is approaching. Those clues come from sensors and sensors are tools that detect changes in the world. When they detect a change, they send a message to the door's brain, which is called a controller. It listens for a sensor to say, something is coming. Then it tells the door's motor to do its job. A motor is a machine that turns electricity into movement. In many sliding doors, the motor spins about or gears that pull the door open and then slide it closed again.

2:10All right, so sensors seem to be the important thing here. Let's figure out how those sensors know you're there. Well, there are different kinds of sensors that automatic doors can use. And one kind of sensor is called radar. Now, have you ever seen those signs on the road that tell you how fast your car is going? Usually put them in areas where they want to make sure that everybody is going the right speed limit. And as your car passes by, the numbers are changing. Do you know how they do that? They use something called radar. Radar sends out invisible radio waves and then listens for them to bounce back.

3:12If something is moving, the bouncing waves change slightly. And that change is called the Doppler Effect. Can you say Doppler? Here's how the Doppler Effect works. When an object moves toward the radar, the returning waves get slightly squeezed closer together. That means the waves arrive a little faster than expected. That is called a higher frequency. But when an object moves away from the radar, the returning waves get stretched farther apart. That means they arrive a little slower than expected. That's a lower frequency. That's how a radar can detect if something is coming closer or moving away. It's just waiting to see how long that bounce takes. That's called the Doppler Effect.

4:12The radar sensor on an automatic door is always looking for higher frequencies. If the radio waves bounce back faster than expected, the sensor tells the motor it's time to open the doors. Now, another common kind of sensor is an infrared sensor. Can you say infrared? Infrared is a type of light you can't see, but you can feel it as heat. Some door sensors are passive infrared, which means they don't shine anything outward. They simply watch for heat patterns. A human body is warmer than many backgrounds, so when a warm shape moves into the area of the infrared sensor,

5:13the sensor notices the change and triggers the door. That's passive infrared, but some doors are active infrared. And active infrared means the door is actually sending out invisible infrared light and checking if it gets reflected back. If you step into the area and reflect the light differently, the sensor detects that change. But no matter which way the sensor is detecting things, it's always just trying to detect a change. If it notices that change, it triggers the controller and the controller triggers the motor. Now, have you ever wondered what happens if an automatic door makes a mistake or closes too quickly? Wouldn't someone get crushed? Those doors are big! How are these things safe?

6:15Well, thankfully, engineers thought about that too. Automatic doors include safety sensors. Many sliding doors have a safety beam, which is an invisible line of light across the doorway. If anything blocks that beam, the controller will keep the doors open or reopen them. If you have a garage with one of those big, loud garage doors, you might notice a little sensor like this near the floor by the door. Ask one of your parents if you have one of these big garage doors. Ask them to show you where that sensor is. But I bet you can find it on your own. It's by the floor because that sensor is there to make sure that nobody's feet are going by. If it detects any kind of movement in that beam, that garage door comes right back open.

7:22Now, why do bigger stores often have these doors, whereas smaller stores usually don't? Well, one big reason is traffic. Big stores have a lot of people coming in and out of them. And if lots of people are coming in and out all day, automatic doors keep that flow moving. When you open a door on your own, you have to stop, open it, and move through it. But an automatic door keeps you walking without having to slow down. And another reason is accessibility. Automatic doors help people who are carrying bags or, you know, if you're at a grocery store, pushing a big cart. Or if you're in a wheelchair. And another big factor is energy. A door that closes reliably helps keep heated or cooled air inside, especially when it's very hot or very cold outside.

8:22That way no one accidentally leaves a door open and lets really hot or really cold air into the building. Of course, automatic doors also cost more than regular doors, and they need maintenance in a way that regular doors usually don't. So a smaller store might just go with a regular door and just make sure it stays closed when it needs to be closed. Alright, so here's how automatic doors work. Sensors detect change. The controller decides what to do about that change and the motor moves the door. A lot is happening every single time you walk into the grocery store or any store that has an automatic door. But you probably don't even notice it. It happens so quickly. Well, now you know what's happening every single time. Isn't that amazing? Alright, let's have a quick quiz.

9:24What is the brain of an automatic door cold? We call it the controller. And what part of the door turns electricity into motion? That is called the motor, and radar sensors send out invisible waves and listen for what? They listen for the waves bouncing back. Alright, let's play truer false. Truer false. Some automatic doors use radar to detect movement. That's true. Truer false, infrared light is always visible to human eyes. No, that's false. Truer false, a safety beam can help stop a door from closing when someone is in the doorway. That is true. Truer false, automatic doors open because they can read your mind.

10:30No, that's false. Can you imagine if a door could open because in your head you just thought, I want that door to open. That would be crazy. Would you rather have an automatic door at your house or your own grocery store just for your family? Oh boy, an automatic door at my house sounds really cool, but a grocery store that was just for my family that just had the things that we like to eat? Ooh, that's hard to say no to. I think I'll go with the grocery store that's just for my family. It would have all the ingredients for homemade pizza. We love to eat homemade pizza around here. My wife makes really good homemade pizza. Alright, let's play what am I? What am I? I make decisions, but I don't have feelings. I receive signals from sensors and I tell the motor when to move. What am I?

11:38I am a controller. The next time you walk into a store and those automatic doors slide open, you can imagine the whole chain of events that's happening in a split second. A sensor notices a change, the controller decides to open and the motor moves the door. Then the safety system keeps watching to make sure the door only closes when you are out of the way. I know something you can do when you go to the grocery store the next time. Look around the top of the doorway. Sometimes you can spot a little dark window or a small box where the sensors live. See if you can find it. We can't see the waves or the infrared light, but sometimes you can see the place where the detecting happens. Pretty cool. What kind of question do you think we'll ask tomorrow on curious kids every day? I can't wait to find out. So until then, keep asking questions and stay curious kids.

12:43And we've got a bunch of birthdays today. Today is Simon's birthday. Simon is from Massachusetts and Simon is turning four. Happy birthday, Simon. Ato is from Tokyo, Japan and Ato is turning seven. Happy birthday, Ato. Alara is from Virginia and Alara is turning six. Happy birthday, Alara. Elias is from Georgia and Elias is turning seven. Happy birthday, Elias. Tucker is from Tennessee and Tucker is turning six. Happy birthday, Tucker. And Kip is from Washington, DC and Kip is turning six as well. Happy birthday, Kip. To all the grownups listening, if your curious kids want their birthdays mentioned on the show, please visit supportcuriouskids.com and join the curious kids club that supportcuriouskids.com. See you tomorrow.