How can someone tell if you are on aeroplane mode?

I connect to the Wi-Fi at home and my dad always wants me to turn my iPhone to aeroplane mode at night. I didn't have it on one night, and he told me to turn it on and that he knew because he could "see it on the thing" and pointed to his phone?
How could he tell? Would this be a security issue? I'm on iiNet Wi-Fi

Most, if not all, home Wi-Fi routers have a screen that lists the connected devices. It's not rocket science, he's just tech literate.

"Airplane mode" means that the Wi-Fi is turned off, simple as that… If you do not have airplane mode on, that means your Wi-Fi is active, and can be seen by the router once you connect. Also, any PC with Wi-Fi software can see your Wi-Fi is on, even if you do not connect to anything.

You router will show a list of connected devices. Easily done by logging into it. Just turn off the Wi-Fi on your phone at night.

What is your father's hang up with your phone being connected to Wi-Fi? Airplane mode turns of ALL wireless connections (cellular, Bluetooth and Wi-Fi) so that they do not interfere with aircraft or hospital systems.

If you don't need the phone on for any offline purpose - music player, alarm clock, diary, etc. - you will be better off turning the whole phone off. If you do need the phone to be on, turn off Wi-Fi and Bluetooth. There's nothing you can really do about the cellular connection.

He can see your phone connected to the Wi-Fi.

When you enable Airplane Mode (on an iPhone in this case) you'd see a plane icon replace the signal bars & carrier name in the top left.

He could have a app to be administrator and see. He also could see u on the Wi-Fi with pc list from a powershell and or command prompt or home group or if your using data from your isp mobile provider. I say it was a guess and your poker face failed u

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