New Member
Hello- Sorry if this is the wrong section.

I really need your help urgently please. I'm traveling back to my home country, and my sister is the quickest way I can get a valid SIM to work there, as I need one upon my arrival to get contacted and picked up by someone, and I'm getting extremely anxious.

My brother is someone I cut contacts with. Long story short, he's someone who would spy on my devices and I always have that paranoia of being watched by him. It's a nightmare I can't seem to escape and it's damaging my brain.

My question is:

If I put my sister's SIM in my phone, use it for phone calls, then take it out and return it to her (whether or not my brother gets his hands on it- who really knows at this point?), will it in any way, shape or form contain any information about me that can be viewed later? For instance, the Facebook account i'm logged into from my phone, Whatsapp, etc. Will any critical information from my phone (which I might later in that visit, connect to a WiFi that also my laptop will be connected to, and my laptop contains very private info) be vulnerable and accessible?

Please help me, and I apologize in advance for the lack of knowledge. I'm traveling after tomorrow.

Thank you so much

Paul Lee

Level 10
I believe you should be alrighty using your sister's sim card, unless someone else has any other input that says otherwise


Level 31
Content Creator
Malware Tester
SIM cards have surprisingly limited memory, so nothing of that could be saved. It only stores contacts and basic phone information. It doesn't store call logs, whatsapp messages whatsoever.


Staff member
You can buy a new PAYG SIM card, and use it to make calls. Most phone contacts are saved to your Google/Microsoft/Facebook accounts, so no need to worry about forgetting the numbers.

If you plan to use WhatsApp, follow these instructions. Otherwise you can continue to use Wi-Fi to make calls with other Apps, without using minutes.

Keep This in Mind
If your sister relies on SMS-based Authentication, then they are at risk, since you are using their Contact Number which will receive this codes. SMS-Authentication is not as secure as other methods, but it's sometimes the only available method for certain online services.
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New Member
The only way from my knowledge to spy on someone using a SIM card would be to redirect the signal through some setup spoof proxy cell tower, like if you are on AT&T you could still use your data, texts, etc, but it would be routed through an access point that your brother setup (not easy to do, and spoof properly) and then direct it to it's original destination.

The purpose of me telling you this is that it's highly unlikely your brother would spy on you using your or your sister's SIM card. Not only because of the complexity of setting up a spoof cell tower, but also in order to get spoofed the compromise might have to occur on your device, and if he can get access to your device to direct to the spoof access point, then there is no reason to really setup a spoof cell tower in the first place.

And he cannot get access to your device through a SIM card, he may be able to track how much data you've used, or texts or call time you've used if he's got access to a carrier account, but he cannot read the contents as there are privacy laws, and I can guarantee you, unless your brother has a PhD in computer science or works for the NSA, he is not spying on you with a spoof cell tower, and if he was, it's likely he would have to compromise your device first, and I'm sure you haven't let him have physical access to your phone.

Worst comes to worst, use a mobile VPN over mobile data, and an app like whatsapp or telegram to call people.

SIM cards have surprisingly limited memory, so nothing of that could be saved. It only stores contacts and basic phone information. It doesn't store call logs, whatsapp messages whatsoever.

Yep, This (y)