How do I know if someone used my WiFi

Hi, Maryposa73, and thanks for reaching out. We see you'd like to know if someone accessed your Wi-Fi network. We'll be glad to assist.

Are you referring to your home Wi-Fi network? If so, that would depend on which modem/router you're using and if it's capable of showing past connections. It will also depend on if you have your network password protected. You'll want to reach out to your router manufacturer to see if it's possible with the hardware you're using. We also recommend taking a look over: Recommended settings for Wi-Fi routers and access points

If you are actually referring to the internet that an iPhone or iPad can share to other devices (aka Personal Hotspot), this connects using your cellular data and not Wi-Fi. This also won't keep a running list of which devices last connected to it. You'd just, again, want to make sure you have a password set up to connect another device to it: How to set up a Personal Hotspot on your iPhone or iPad

If we've misunderstood your concern entirely, please feel free to reply back to this post with more specific details please.

Cheers!