To close apps on an iPhone without a home button, swipe up from the bottom of the screen and pause in the middle to reveal the App Switcher, then swipe up on the preview of any app to close it; you can swipe multiple apps at once with multiple fingers. This gesture replaces the double-click home button action on older iPhones and allows you to manage your running applications.
iPhone X and later
Three-finger gestures on iPhone primarily activate accessibility features like VoiceOver (for screen reading and navigation) and Zoom (magnification), allowing scrolling, zooming, and text manipulation (copy/paste/undo) with specific taps and drags, though some text actions work without VoiceOver enabled for quick editing. Common gestures include three-finger double-tap to toggle VoiceOver speech, triple-tap for the screen curtain, and pinching/spreading with three fingers for copy/paste actions, notes this YouTube video.
Set up Assistive Access on iPhone
*3001#12345#* on an iPhone activates the hidden Field Test Mode, a diagnostic tool for network engineers and power users to see detailed cellular data like signal strength (dBm), cell tower info, and network quality, accessible by dialing the code in the Phone app and pressing call, often after turning off Wi-Fi for accurate cellular readings.
You should only close an app in the quick-launch (App Switcher) screen if it is "misbehaving" - not working right, or if it is using energy (as per Settings/Battery) and you don't need it at the present time. There are several reasons you should not close apps.
The Main Apps That Eat Battery
From the Home screen, tap the Recents icon to the left of the Home button. All of your active or opened apps will be listed. If you've customized your Navigation bar, Recents may be located on the right, unless you're using full screen gestures. To open an app, simply tap it.
Learn more about Google Play services.
On other iPhones, you swipe up on the app card. On the iPhone X, you press and hold on the cards until a red (-) symbol appears in the corners. Tap those to close the apps. It's very similar to the way you delete apps from your home screen.
Hidden Battery Power / Boost Signal Strength
By pressing *3370# or #3370#, you'll activate your phone's “reserve battery power”. Battery life will increase by 50%. The reserve will automatically charge up the next time you change your device. Other claims state dialing the same sequence will boost cellular reception.
Number to dial to see if your iPhone is tapped
Dial *#21# to check if a third party intercepts your calls, messages, or other data. This code will tell you if services like voice, data, fax, SMS, and others are being forwarded to another number.
Call barring allows you to block certain types of incoming or outgoing calls. Dialing *#33# displays your device's current call barring status. If you're receiving excessive spam calls, enabling call barring can help prevent unwanted calls, including those from potential hackers.