Intro: Glue Your RFID Card to Phone
I superglued my school ID card to my phone.
Why you ask? Well, as student at UC Berkeley many of my buildings, labs, and rooms are RFID access only. Our student ID is the cardkey. But that means anytime I want to go between labs or buildings I have to take my card or wallet. I was often leaving my card in the lab, or taking it out of my wallet only to lose it.
My student ID serves serves four daily purposes: cardkey, bus pass, gym access, and photoID. Student or not, you may relate to this regular need for a single RFID card.
Turns out, we seem to have our phones with us 24/7. A recent poll showed most people cannot go a single day without their phone. Well gone are the days of losing my card! Simply put, I super glued my ID to my phone.
Step 1: Background & Materials
Why not get one of those phone-wallet things? I'm very minimalist when it comes to my phone. I hate cases and added bulk. I needed the slimmest way to attach a single RFID card permanently to my phone. Turns out this is non-trivial.
Gluing an RFID card straight to your phone will render it useless.
Eager as I was, I promptly glued my card to the phone only to find the RFID card no longer worked on any of the readers. Looking into my mistake, a metal backing placed flush against the RFID tag essentially couples with the antenna to form a Faraday cage. Wikipedia tells me that Faraday cages can attenuate RFID. Okay so I need to break the coupling effect. Luckily, this mistake also showed me that superglue, even when hardened, can be easily removed from the anodized aluminum iPhone backing.
- Clean cell phone (my is an iPhone 5s with the anodized aluminum back)
- Gaffe tape
- Xacto Knife or Scissors
- Wet paper towel handy
Step 2: Tape & Glue Your Card
- Test your card
- I did this project near a representative card reader since they vary in strength.
- Hold your card flush against the phone and try to get the reader to detect it
- If it doesn't detect the card then you need to add something between the phone and the card
- If the reader works, go ahead and glue! I make no promises it will still work afterwards
- Layer with tape and repeat Step 1
- With the photo side down, I laid a single layer of gaffe tape side-by-side, leaving overlap.
- I tried various materials and numbers of layers to break the coupling between the phone and the card. I tried a thin aluminum mesh, copper tape, duct tape, and gaffe tape. For me, two layers of gaffe tape works!
- Trim & Glue
- Using the Xacto knife I trimmed the sides
- Then I cut small pocket in the corners for the glue. In hindsight, I wouldn't do this again. The gaffe tape has held well for months
- Place (4) generous spots of glue in the corners of the card and press firmly to the middle of the back of the phone.
- For a weaker and more temporary adhesion, you could use hot glue!
- Wipe excess glue
- Use the wet paper towel to quickly wipe the excess glue, leaving a clean finish.
Step 3: Success!
This simple project really has helped my lost-wallet & locked-out situation. I'm rarely without my phone so when I leave a locked building I only need to check that I have my phone and nothing else. Plus if I lose my phone, iPhone has the Find My Phone feature. Plus, I learned a bit about RFID shielding.
In the case of UC Berkeley, I sacrificed two pieces of information: the card ID and the barcode. In the months attaching my card, I have only needed my barcode once (to get the new bus pass) and instead they just read my student number.