Guidance on building a locking system

Projects General Guidance
1

I am looking to build a locking mechanism that would maintain a soleniod valve unenergized in the unlock position and energized in the lock position. I need it to lock when the rfid is aproximetely 4 foot away from it and unlock at closer proximity. I watched the youtube video on the card reader to soleniod door lock project that your company posted. I am looking to achieve that result but not having to place the card an inch from the board for activation. Do you have a reader or key fob reader that could get me within the distance parameters?

Long story short you walk away from the reader and the lock engages the locking mechanism automatically. I appreciate any guidance you can provide.

2

Use the magnifier symbol up to the right, in this window, and search for "Arduino + RF".
What You ask for, I doubt You will find. RF is not designed for scanning crowds at distance.

3

There's RFID out there that can read at much greater distance than a few cm.

By nature of RF you can not determine the exact range, so you can't have it cut off at exactly 4ft or so. You can limit the transmission power to have a range of roughly that, but the actual range will depend big time on how the RFID card is carried: in a badge visible on the chest or in a wallet in the back pocket of the pants will make a huge difference in effective range.