How to make Wi-Fi ask for password everytime?

I noticed that when accessing Internet on wireless laptop or iPhone, it doesn't ask for password to access. My question is if others come into my house, can they access the Internet? If so, please let me know if there's a way to setup the password to prevent this?

Your device remembers the password so you don't have to reenter it every time you connect.

Any device not previously connected to your secured Wi-Fi network will prompt for a password.

Your phone and laptop automatically provide the password each tine you connect visitors' devices won't have the password.

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If other come to your house and try to connect to network they won't be able unless they type a password,
So if people don't know password they can't use internet.

Depends on the security setup of your Wi-Fi router, If it is setup as Open Security, then no password will ever be required by anyone.

If one of the security options is enabled, then a paasword is required. If toy have already entered this password, your device will probably remember it so it will not ask you, but it will ask any others who attempt to use your Wi-Fi network.
If you don't know if your system is password enabled, delete the network connection on your portable device and reconnect. IF a password is required, you will see a prompt to enter the password. On most Wi-Fi modems the factory preset password is printed on a sticker on the bottom of the modem with the network SID name.
The network name and password can be changed by accessing the Wi-Fi router control panel. This is easy to do, but you need the IP address of the router that you will enter into your browser. If you don't know this do a Google search on your router model with the word login and /or control panel and you should get some clear instruction.
Netgear modems as well as others allow a guest network, that you can activate from the control panel with or without a password. Netgear also offers software that works with your router to tell you who is logged into your network, They call this Netgear Genie, works great and you can change network name and password without logging into the modem directly. Free download.