Contact vs Contactless CAC Readers Explained

CAC readers come in two main types: contact and contactless. Understanding the differences helps you choose the right reader for your work environment—and explains why some readers work with certain systems while others don’t.

How Contact CAC Readers Work

Contact readers require physical insertion of your CAC into a slot. Gold contacts on the card touch metal pins inside the reader, creating a direct electrical connection. This connection transmits data between your card’s chip and your computer.

Common contact readers include:

• SCR3310v2 (most widely issued)
• Identiv SCR3500
• HID Omnikey 3121
• ACS ACR38U

How Contactless CAC Readers Work

Contactless readers use radio frequency (RF) technology to communicate with your card without physical contact. You tap or hold your CAC near the reader, and it reads the card through electromagnetic induction.

Common contactless readers include:

• HID Omnikey 5427 CK
• Identiv uTrust 3700 F
• ACS ACR1252U

When You Need a Contact Reader

Contact readers are required for:

• PKI Authentication: Logging into DoD websites, signing documents, and email encryption all require reading the PKI certificates stored on your card’s contact chip
• Most government computers: Standard NIPR and SIPR workstations expect contact reader authentication
• VPN connections: Remote access typically requires contact-based certificate authentication
• Digital signatures: Signing documents with your CAC requires the contact interface

When You Need a Contactless Reader

Contactless readers are used for:

• Physical access control: Building entry systems, secure doors, and turnstiles read the contactless chip
• Quick badge checks: Security checkpoints where speed matters
• Vending and cafeteria systems: Some installations use contactless CAC for payments
• Time and attendance: Clock-in systems at some facilities

Dual-Interface Readers: Best of Both Worlds

Some readers support both contact and contactless interfaces in one device. These are useful if you need both capabilities without switching readers.

Popular dual-interface options:

• HID Omnikey 5422 (contact + contactless)
• Identiv uTrust 4701 F Dual
• ACS ACR1281 (contact + dual-interface cards)

Which Type Do Most People Need?

For typical DoD employees and contractors working on computers, a contact reader is essential. This is what you need for:

• Logging into your government computer
• Accessing OWA and other DoD websites
• Signing and encrypting email
• Remote VPN access
• Any PKI-based authentication

Contactless readers alone won’t work for these tasks because the PKI certificates live on the contact chip, not the contactless chip.

Understanding Your CAC’s Two Chips

Your CAC actually contains two separate chips:

• Contact chip (gold square): Stores your PKI certificates, allows digital signatures, and handles computer authentication
• Contactless chip (hidden inside): Contains a unique identifier for physical access, cannot perform cryptographic operations

These chips don’t share data. A contactless reader cannot access your certificates, and a contact reader cannot open building doors.

Troubleshooting by Reader Type

Contact reader not working?

• Check for dirty or damaged contacts on the card
• Clean the reader slot with compressed air
• Ensure the card is inserted with the chip facing the correct direction
• Verify drivers are installed for your specific reader model

Contactless reader not working?

• Hold the card closer to the reader (within 1-2 inches)
• Remove the card from thick wallets or holders that may block RF signals
• Check if multiple cards are interfering (remove other smart cards from your wallet)
• Verify the system actually uses contactless—many require contact readers

Buying Recommendations

For home/remote work: Get a contact reader like the SCR3310v2 or HID Omnikey 3121. These cover all standard DoD computer authentication needs.

For mobile workers: Consider a compact USB contact reader that travels easily, such as the Identiv SCR3500 A.

For IT administrators: Dual-interface readers provide flexibility for testing and supporting users with various needs.