How to Detect Unauthorised Devices on Your Network
Every IT team has the same uncomfortable realisation at some point: there are devices on the network that nobody authorised, nobody documented, and nobody is managing.
These devices can come from numerous sources, like:
- a personal laptop plugged into an office port
- a wireless access point someone brought from home
- an IoT sensor a facilities team installed without telling IT
- a forgotten test server still running in a closet.
These unauthorised devices represent one of the most common and underestimated security risks in enterprise networks. They sit outside your patching cycle, your endpoint protection, and your compliance reporting - and until you can reliably detect them, you cannot manage the risk they create.
Why Unauthorised Devices Are a Bigger Problem Than Most Teams Realise
The scale of unauthorised devices - and the issues they create - have grown substantially in recent years.
The proliferation of IoT devices, the normalisation of hybrid work, and the ease of connecting personal hardware to corporate networks have all contributed to an environment where rogue devices are the norm.
Research consistently shows that a significant number of employees use personal, non-company devices for work, and many organisations allow these unmanaged devices to access corporate resources with minimal controls.
But an unauthorised device can introduce malware into a network segment that was otherwise well-defended. It can serve as an entry point for lateral movement if compromised. It can exfiltrate data without being subject to data loss prevention (DLP) policies. And it creates a gap in your compliance posture - most frameworks, from CIS Controls to ISO 27001 to Australia's Essential 8, require organisations to maintain a complete and accurate inventory of hardware assets.
An unknown device is, by definition, a compliance failure.
IoT devices are a particular concern. Many connect to the network with default credentials, run outdated firmware, and have limited or no support for endpoint security agents. With IoT-related attacks reaching staggering global volumes, these devices significantly increase an organisation's risk surface.
Common Ways Unauthorised Devices Appear on Your Network
Understanding how rogue devices end up on your network is the first step towards detecting them.
The most common paths include:
- personal devices connecting via Wi-Fi or Ethernet (phones, laptops, tablets brought by employees or visitors)
- IoT and operational technology installed by non-IT departments - smart displays, environmental sensors, IP cameras, badge readers
- consumer networking equipment - personal routers, switches, or wireless access points that create uncontrolled network segments
- shadow IT infrastructure - development servers, NAS devices, or Raspberry Pi boards set up for one-off projects
- legacy hardware that was decommissioned on paper but never physically removed from the network.
Each of these categories has a different risk profile, but they share a common trait: they're invisible to your management tools unless you actively look for them.
How to Detect Rogue Devices
Effective rogue device detection comes down to two capabilities: knowing what should be on your network, and continuously checking what actually is on your network.
Maintain an authoritative asset inventory
You need a baseline of known, authorised devices - including their MAC addresses, IP assignments, device types, and locations. Without this baseline, you have no reference point for identifying what doesn't belong.
Manual inventories fall behind almost immediately, which is why automated discovery is essential for any network of meaningful size.
Run regular network scans
Agentless network scanning discovers every device with an IP address on your network, whether or not it has an agent installed or is part of your management domain. Scans should cover all subnets, including those used by guest networks, IoT segments, and operational technology.
Frequency matters - a monthly scan will miss devices that connect temporarily, while daily or continuous scanning catches transient connections.
Compare scan results against your baseline
The value of a scan is in the delta. When a device appears that isn't in your authorised inventory, it should be flagged automatically. The response might be as simple as verifying that a newly provisioned device was not yet added to the Configuration Management Database (CMDB), or you may discover something that requires immediate investigation.
Segment your network
VLANs and network segmentation limit the blast radius of any unauthorised device. If a rogue device connects to a well-segmented network, its ability to reach sensitive resources is constrained.
Combine segmentation with 802.1X port-based authentication where practical to prevent unauthorised devices from obtaining network access in the first place.
Monitor for anomalous behaviour
Even with scanning in place, behavioural monitoring adds a layer of defence. Unusual traffic patterns - like unexpected outbound connections, scanning activity, or communication with known malicious IPs - can indicate a compromised or malicious device that might otherwise blend in.
What to Do When You Find an Unauthorised Device
Detection is only half the equation. You also need a defined process for handling unauthorised devices when they're discovered.
Start by triaging. Not every unknown device is a threat - some are legitimate devices that were simply not added to the inventory. The goal is to identify the device, determine who connected it and why, and decide whether it should be authorised, quarantined, or removed.
For devices that should not be on the network, disconnect them and investigate. Determine how the device obtained access and close the gap. If it connected via an unsecured port, implement port security. If it joined via Wi-Fi, review your wireless authentication policies.
For devices that are legitimate but were not previously tracked, add them to your inventory and bring them under management - apply patches, configure endpoint protection, and assign an owner.
Document everything. Rogue device incidents provide useful data for improving your security posture over time. Patterns in how unauthorised devices appear will point to process gaps or policy weaknesses that need attention.
How Open-AudIT Helps You Find Unauthorised Devices
Open-AudIT v6.0 is built for exactly this challenge. It performs agentless discovery across your entire network, identifying every device with an IP address including servers, workstations, network equipment, printers, IoT devices, and anything else that is connected.
Because it is agentless, Open-AudIT discovers devices regardless of whether they have management software installed, which is precisely the point when you're looking for hardware that hasn't been through your provisioning process.
Each discovery scan is compared against your existing inventory, with new and changed devices flagged automatically. Open-AudIT records device type, operating system, MAC address, open ports, installed software, and hardware details, giving you the context needed to quickly determine whether a device is authorised.
For organisations managing compliance obligations, the platform maps discovered assets against frameworks including CIS Controls, ISO 27001, and Australia's Essential 8.
Get Started With Open-AudIT
You cannot secure what you cannot see. Open-AudIT's free Community edition lets you discover up to 100 devices and start building a complete, accurate picture of what is actually on your network.