Two Different Things Called "OT Security Monitoring"
When people talk about OT security monitoring, they usually mean one of two quite different things, and the distinction is worth being clear about before you spend budget or political capital on either.
The first is network-based monitoring: deploying sensors on your OT network that passively observe traffic, identify assets, detect anomalies, and alert on suspicious behaviour. Dragos, Claroty, Nozomi Networks, and similar vendors operate in this space. These are sophisticated tools that can do things like detect unusual PLC command sequences, identify rogue devices on the network, or spot lateral movement.
The second is intelligence-based monitoring: tracking what's being publicly disclosed about the vendors and products you use — CVEs, ICS advisories, vendor patch notices, KEV entries — and alerting you when something relevant comes out. No sensors. No network access. No agents on anything.
OTWarden is in the second category. This post is about what that means in practice — what it can and can't do, and where it fits alongside other security measures.
Why Network-Based Monitoring Is Hard to Deploy on OT
The vendors in the network monitoring space are good at what they do. The technology works. The problem is operational, not technical.
Installing passive monitoring sensors on a live production environment — a chemicals plant, an offshore platform, a power substation — involves change management, engineering sign-off, and often vendor approval (some automation vendors make it explicit in their support contracts that unauthorised devices on the network can void warranties or support agreements). For a plant that runs continuously, even read-only changes to network infrastructure go through a rigorous approval process, and rightly so.
Then there's cost. Enterprise OT monitoring platforms are enterprise-priced. The deployment, integration, and ongoing support costs put them firmly in the category of tools that large organisations with dedicated OT security teams can justify, and many smaller operators simply cannot.
None of this means network monitoring is wrong or unnecessary. It means there are real constraints on when and whether it's deployable — and for a lot of OT environments, those constraints are binding.
What Intelligence-Based Monitoring Actually Covers
Without touching your network, intelligence-based monitoring can tell you:
- When a CVE is published that affects products on your watchlist — by vendor, product line, or sector
- When that CVE appears in CISA's Known Exploited Vulnerabilities catalogue, meaning it's being actively exploited in the wild
- What the vendor's recommended remediation is and whether a patch is available
- When EPSS scores indicate an as-yet-unexploited vulnerability is attracting attention that suggests exploitation is likely
- When advisories are revised — sometimes CISA or a vendor updates an advisory to add affected versions or change the severity
What it cannot tell you:
- Whether that vulnerability is actually present in your specific configuration (you need an asset inventory and version records for that — OTWarden has an asset inventory feature to help bridge this gap, but it relies on data you provide)
- Whether anyone is actively exploiting it on your network right now
- Whether you have unusual traffic patterns, rogue devices, or anomalous behaviour inside your environment
These are real limitations. Intelligence-based monitoring is not a replacement for network monitoring when network monitoring is feasible and warranted.
Who This Approach Is For
The honest answer is: most OT operators, at least as a starting point.
If you're running a mid-sized manufacturing site, a water treatment facility, a smaller port or terminal — you probably don't have a dedicated OT security team. You might have one person who covers both IT and OT. You almost certainly aren't running Dragos or Claroty. But you are running Siemens, Schneider, Rockwell, or ABB equipment, and CISA is publishing advisories about that equipment regularly.
Intelligence-based monitoring makes sense here as a foundation — knowing what's being disclosed about your vendors' products, filtered to what's relevant to you, delivered to your inbox when it matters. That's a meaningful improvement on not knowing, and it costs a fraction of network-based tooling.
For larger organisations that do run network monitoring platforms, the two approaches are complementary. The CISA advisory pipeline and your internal telemetry answer different questions. You need both.
How OTWarden Works in Practice
OTWarden monitors CISA ICS advisories, the CISA KEV catalogue, and vendor feeds from Siemens, Rockwell, Schneider, BSI, and NVD. You set up a watchlist by vendor, product, or sector. When something relevant is published, you get an email with the advisory details, severity, EPSS score, KEV status, and a link to the full advisory.
There's no agent to install, no network access required, no integration with your OT environment. Setup takes a few minutes. The 14-day trial is free and doesn't require a card.
It's a narrow tool that does one thing: makes sure you're not missing advisories about your kit. That's genuinely useful, and it's honest about what it is.