I’m a newbie, I need a little advice

So, I am a private investigator. I am not a hacker, Programmer, Or geek by any extent of the imagination. Sometimes I have to be inside of a gated community very early, and I want to know if I can use the Flipper zero to capture the RFID signal when a resident enters and then use it to mimic the RFID signal to gain entry?

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This is really not how it works.

It is called NFC (Near Field Communication) for a reason. With a Proxmark3 you could add an bigger antenna to get approx. 35 cm range. But with the Flipper, depending on the transmission format 4 to 10 cm are maximum in my tests.

Even if you are able to capture the card, a lot of them are very picky with the trimmings. So you’ll have a perfect dump, but you can’t emulate it due to physical restrictions. But as workaround you could write the dump to a blank card and use this one.

Than we have the standards. ISO 14 a or b, ISO 15, FDX-B, … Yes, even FDX (134KHz animal tag) could get you access through a pet door to the house.

… There is a lot to the investigate for you. But you can’t just hold the Flipper on a reader and magically it opens the door.
For beginners (non tech people) learning pick locking will be easier.

Let’s say you are lucky and got an easy Mifare Classic. Easy to crack. Just read out, find you are missing keys, go to the reader, capture roundabout 10 nonces, put your dump and the captured nonces to your laptop and let crack the missing keys (darkside, hard nested, …) … It is math, so it could be cracked in 10 seconds or 30 minutes or an hour.

And some cards got a counter. Even if you’ll get access, the counter will go up, and the owner can’t access anymore. And will check his/her CCTV.
And there are java based smart cards. They will only provide a challenge response, calculated within the card in a secure element. No way to get access, regardless of how cool your toys are. Maybe over a reply attack.

Just a brief summary.