eli5:How is a SIM card identified as switched off and not just outside of a phone instead?


Like, I lost my sim card. I’m sure it’s somewhere in my home. I have a ton of old phones. When I call the number it says switch off, I wanna know if it’s the same even if the sim is outside of a mobile? How does it all work.

In: Technology

If you let your provider switch it off it will be deleted in their systems. When you just take it out of the phone the system will still know that it is active and just not connected currently.

A Sim card is nothing else but an ID. Provider system checks sims against a list. If its not on the list, its switched off.

does it say “the phone is switched off” or a different message? It’s quite likely that it’s just a generic network message. they can’t see if a sim is in a turned-off phone or if it’s sat on a shelf, they just know they can’t connect to a phone that has that sim card in it

it’s “switched off” because there is no phone worldwide that has your SIM installed, and is switched on.

So, yes it’s the same. The SIM is a very small computer chip that is powered by the phone, and is used to identify the phone towards your mobile network, such that it can recieve calls to “your number”.

SIM card is just an identifier with serial number that allows your phone to connect to network. Phones can connect to network even without SIM card but they don’t have access to any advanced features of the network (SMS, internet and such) but you can still call 911 even without SIM.

When you put SIM card into the phone it tells that network “hey I belong to you, here’s my serial number to prove it, give me access to advanced features and allow me to contact other users”.

SIM card is registered in the system of the network and assigned to your account and when someone calls your number the network checks is your SIM is in range and if it is then your phone rings.

If the phone is turned off or SIM card is out of the phone then network can’t see it and you get the message that your number is unavailable. SIM card is nothing more than a passport that allows your phone the access to network.

If you lose a SIM card and get a replacement then all the network does is delete the old serial number of old SIM card and assigns the new serial number of the new card to your account.

You can also have 2 SIM cards with the same number in some networks but only one can be active at any time. Because they are connected to only one account only the last SIM card that you used will be the one that the sistem will try to reach. So if you have 2 phones with 2 SIM cards with same number when someone calls you the phone that rings will be the one that you used last to call someone because that phone was the last one to “speak” with the network.