Choosing a CAC Reader: The Only Two That Matter

Visit any military exchange or browse Amazon for CAC readers and you’ll find dozens of options. Don’t waste your time. For reliable DoD smart card access, two readers dominate the approved lists and real-world reliability: the SCR3310 and the ACR39U. Everything else is either a rebranded version of these or significantly less reliable.

This comparison covers which reader fits your specific use case.

SCR3310v2.0 Overview

The SCM Microsystems SCR3310v2.0 has been the government workhorse for over a decade. If you’ve used a CAC reader in any federal building, chances are it was an SCR3310 or its predecessor.

Pros:

• Near-universal compatibility across all Windows versions
• Proven reliability with millions of units deployed
• Compact vertical design fits in laptop bags easily
• No driver installation needed on Windows 10/11
• GSA-approved and on most agency procurement lists
• Price point around $15-25

Cons:

• USB 2.0 only (adequate for CAC, but dated)
• Vertical insertion can be awkward on cluttered desks
• Older units may have worn contact pins
• Limited indicator lights (hard to tell if card is reading)

The SCR3310 uses USB 2.0 full speed, which provides plenty of bandwidth for smart card operations. Despite its age, the design remains effective. The vertical form factor keeps your CAC visible and accessible.

ACR39U Overview

The ACS ACR39U is the modern challenger, offering updated electronics and improved Linux compatibility. It’s become the recommended reader for Mac users and teleworkers who need cross-platform support.

Pros:

• Excellent macOS and Linux compatibility out of the box
• Horizontal insertion feels more natural to most users
• Clear LED indicators for power, card, and data activity
• More robust contact mechanism than aging SCR3310 designs
• USB 2.0 with USB-C variants available
• Better suited for Chromebook compatibility (where supported)

Cons:

• Slightly larger footprint than SCR3310
• Price typically $5-10 higher than SCR3310
• Some older Windows systems need manual driver installation
• Less ubiquitous in government settings (fewer spare cables available)

The ACR39U’s horizontal card slot accommodates cards without bending the cable—a real advantage on cramped desks. The LED indicators provide immediate visual feedback when your card is being read.

Which Reader Should You Buy?

Buy the SCR3310 if:

• You only use Windows systems
• Your organization already uses SCR3310 (easier IT support)
• You want the cheapest reliable option
• You prefer a proven, conservative choice

Buy the ACR39U if:

• You use Mac or Linux alongside Windows
• You prefer horizontal card insertion
• You want visual LED feedback on card status
• You’re setting up a new telework station

What About Other Readers?

Built-in laptop readers: Some Dell and Lenovo business laptops include integrated smart card readers. These work fine when functional but are expensive to repair if they fail. Having a backup USB reader is advisable.

Keyboard-integrated readers: Cherry and others make keyboards with built-in readers. The readers themselves are usually SCR3310 internals, so they work well. Convenient if you’re buying a new keyboard anyway.

Cheap no-name readers: That $8 reader on Amazon probably uses cloned firmware that may work initially but often fails after Windows updates or simply stops working randomly. The $10-15 savings isn’t worth the frustration.

Mobile/Bluetooth readers: Products like the Tactivo exist for tablet and phone use. Compatibility is limited and constantly changing. Only consider these if mobile CAC access is a specific requirement.

Purchasing Recommendations

Buy from reputable sources to avoid counterfeits. Amazon sells legitimate readers, but verify the seller is authorized. Government employees can often obtain readers through their IT department or RAPIDS office.

Consider buying two readers—one for your primary workstation and one for backup/travel. Reader failure always happens at the worst possible time. Having a tested backup eliminates that emergency.

Reader Lifespan and Replacement

Quality CAC readers last 3-5 years with regular use. Signs a reader needs replacement:

• Increasing card read failures
• Visible corrosion on contacts
• Loose USB cable connection
• Bent or missing contact pins

When your reader starts showing these signs, replace it proactively. A $20 reader replacement beats missing a deadline because you can’t authenticate.

Either the SCR3310 or ACR39U will serve you well. The “best” reader is the one that works reliably with your setup—pick the one that fits your platform and workspace.