Managed SIEM (SIEM-as-a-Service): Run Detection Without Running the Platform
A Security Information and Event Management platform is one of the most powerful tools in a security program — and one of the most demanding to operate. Managed SIEM delivers continuous log collection, correlation, and alert monitoring without requiring your team to deploy, tune, and maintain the platform. Detection outcomes without platform operations overhead.
What Managed SIEM (SIEM-as-a-Service) Is
Managed SIEM is a model in which a security provider deploys, operates, and continuously optimizes a SIEM platform on your behalf. Your organization gains the full detection capability of a mature SIEM — log ingestion from every relevant source, correlation rules tuned to your environment, 24/7 alert monitoring, and compliance-ready audit log retention — without the engineering burden of building and running the platform internally.
The distinction matters because a SIEM is not a product you deploy once and forget. It is an operational system that requires continuous tuning, log source onboarding, rule development, false positive reduction, and analyst coverage to deliver value. Organizations that buy SIEM licenses without the operational resources to run them consistently end up with an expensive log aggregator that generates alerts no one investigates. Managed SIEM solves the operations problem, not just the tool problem.
Armorstack SENTRY delivers managed SIEM as a core component of the SENTRY MDR program — not as a standalone log storage product, but as the detection engine at the center of a 24/7 security operations program. The SIEM is managed; the alerts it generates are investigated by SENTRY analysts; the evidence it produces is formatted for your compliance requirements.
Build Your Own SIEM vs. Managed SIEM: What the Decision Actually Involves
Most mid-market organizations that evaluate SIEM are really evaluating two questions simultaneously: which platform, and who operates it. The build-vs-buy question is often framed as a cost question, but the deeper issue is operational capacity.
What Building Your Own SIEM Actually Requires
Running an in-house SIEM is not a matter of purchasing a license and importing logs. A mature, effective in-house SIEM requires:
- SIEM engineering resources to design the log architecture, onboard log sources, and write detection rules specific to your environment.
- Ongoing tuning effort to reduce false positive rates as your environment changes. A freshly deployed SIEM in an average mid-market environment can generate hundreds of alerts per day, most of which are noise. Without continuous tuning, alert volume grows faster than analyst capacity to review it.
- Log source management for every system generating security-relevant events — network devices, endpoints, cloud workloads, identity systems, applications, and OT assets. Each log source requires configuration, monitoring for gaps, and periodic review to confirm coverage has not drifted.
- 24/7 analyst coverage to actually review what the SIEM surfaces. A SIEM that generates an alert at 2 AM that no one reviews until 9 AM the next business day has provided minimal security value for that seven-hour window.
- Storage and retention management aligned to your compliance framework’s requirements — HIPAA audit log retention, PCI-DSS 12-month online and 12-month archive, CMMC AU family requirements.
- Platform maintenance — software updates, infrastructure management, capacity planning as log volume grows.
For organizations with a dedicated security engineering team and an existing 24/7 SOC function, in-house SIEM is a reasonable path. For most mid-market organizations, that is not the reality.
What Managed SIEM Provides Instead
Managed SIEM shifts the operational burden to the provider while preserving the detection outcomes your compliance program and security posture require. Under the managed model:
- Armorstack engineers deploy and configure the SIEM platform against your environment’s specific architecture.
- Log source onboarding is handled by the SENTRY team — every relevant source, configured correctly, with gap monitoring to detect when a source goes silent.
- Detection rules are developed by security engineers who understand your vertical’s specific threat landscape and compliance requirements, then continuously tuned to reduce noise without sacrificing coverage.
- SENTRY analysts monitor the SIEM alert queue 24/7/365 — not a dashboard your team checks in the morning, but a live operating environment staffed continuously.
- Log retention is configured to your framework’s specific requirements from the start, with evidence packages structured for audit and examination review.
The Cost Reality
SIEM platform licensing — Splunk, Microsoft Sentinel, IBM QRadar, Exabeam, LogRhythm, and others — is typically priced by data ingestion volume, endpoints monitored, or a combination of both. Licensing cost is only part of the total cost picture. Implementation, ongoing engineering, storage, and analyst staffing are the majority of the operational spend. Managed SIEM typically consolidates all of those costs into a single, predictable engagement. For a specific cost comparison for your environment, Armorstack scopes every SENTRY engagement individually — the right starting point is the 90-Day Proof or a direct scoped assessment. Published per-seat or per-GB rates for this type of engagement are misleading, because the cost drivers are specific to your environment’s log volume, source count, and compliance requirements.
What Managed SIEM Ingests: Log Sources and Coverage
A SIEM is only as effective as the log sources feeding it. One of the most common failures in in-house SIEM deployments is incomplete coverage — the platform is deployed and tuned for a subset of the environment, creating blind spots that threat actors exploit. Managed SIEM under SENTRY is scoped to cover the full relevant attack surface.
| Log Source Category | Examples | Security Value |
|---|---|---|
| Endpoint / Server | Windows Event Logs, Linux syslog, macOS unified logs, EDR agent telemetry | Process execution, logon events, privilege escalation, lateral movement indicators |
| Network Infrastructure | Firewall logs, IDS/IPS alerts, DNS query logs, DHCP logs, NetFlow | C2 communication, data exfiltration, anomalous traffic patterns, beaconing |
| Identity and Access | Active Directory / Azure AD, LDAP, MFA platform logs, PAM systems | Credential abuse, impossible travel, privilege changes, service account anomalies |
| Cloud Platforms | AWS CloudTrail, Azure Monitor, GCP Cloud Audit Logs, M365 audit logs | Unauthorized resource creation, storage bucket access, IAM changes, API abuse |
| Email Security | Microsoft Exchange / Defender, Google Workspace, SEG logs | Phishing delivery, BEC indicators, mail rule manipulation, attachment detonation |
| Applications | EHR audit logs (Epic, Oracle Health), ERP systems, web application logs | Anomalous ePHI access, bulk data queries, application-layer attacks |
| OT / ICS | SCADA system logs, historian data, PLC event logs, ICS network sensors | Unauthorized command execution, protocol anomalies, OT/IT pivot indicators |
| Physical Security (via CITADEL) | Access control system events, video analytics alerts, building management system logs | After-hours access, tailgating indicators, physical-cyber correlation events |
| Vulnerability / Patch Management | Vulnerability scanner results, patch management platform logs | Active exploitation of known vulnerabilities, unpatched system exposure tracking |
Log source scope is determined during the SENTRY onboarding process and is specific to your environment. Not every organization requires every category — the scoping process identifies which sources are relevant to your compliance obligations and threat profile.
Managed SIEM and Compliance Log Retention
For organizations in regulated industries, log retention is not a best practice — it is a specific, auditable requirement. One of the most common compliance gaps Armorstack identifies during assessments is organizations that have log sources generating events but no structured retention program that satisfies the framework’s specific requirements for duration, integrity, and accessibility.
Retention Requirements by Framework
The table below reflects publicly documented retention guidance from each framework. Your specific implementation requirements depend on your scope, your systems, and your organizational risk tolerance. Consult your compliance program documentation or Armorstack’s VERITY advisory team for a complete mapping.
| Framework | Relevant Requirement | Retention Guidance |
|---|---|---|
| HIPAA Security Rule | § 164.312(b) Audit Controls; § 164.530(j) Documentation requirements | Audit logs must be retained for six years from date of creation or last effective date. OCR guidance strongly implies active monitoring capability, not passive retention only. |
| PCI-DSS v4.0 | Requirement 10.5 — Audit log history is retained and available for analysis | At least 12 months of audit log history, with at least the most recent three months available for immediate analysis. Immutability controls (Req. 10.3) required to prevent log modification. |
| NIST SP 800-171 / CMMC 2.0 | AU.3.046 — review and analyze audit logs; AU.3.048 — collect audit information | NIST SP 800-171A assessment procedures require demonstrating that audit records are retained in accordance with organizational policy. CUI system audit logs: organizational policy, typically 1-3 years in DIB practice. |
| SOC 2 Type II | CC7.2 — monitor for anomalies; CC7.3 — evaluate security events | No specific retention duration mandated by the TSC. Auditors assess whether the monitoring program is sufficient and continuous. Most SOC 2 engagements expect at least 12 months of log history accessible during the audit period. |
| GLBA Safeguards Rule | 16 CFR Part 314.4(h) — monitoring and testing safeguards | The rule requires monitoring for unauthorized access and testing safeguards regularly. No specific retention duration is mandated, but examination readiness typically requires demonstrating historical monitoring data. Federal banking examiner expectations vary by agency. |
SENTRY’s managed SIEM configures log retention aligned to your primary compliance framework from the start of the engagement. Retention configuration, storage integrity controls, and evidence packaging are built into the program — not retrofitted for audit season.
Frequently Asked Questions About Managed SIEM
We already have a SIEM license. Does managed SIEM mean we have to replace it?
Not necessarily. Managed SIEM can mean operating the platform you already own, rather than requiring you to adopt a new one. If you have a Splunk, Sentinel, or QRadar deployment that is underperforming — too many false positives, incomplete log coverage, no one reviewing alerts consistently — the problem is often operational, not technological. SENTRY can take over the engineering and operational functions of your existing platform rather than treating the engagement as a replacement project. During the scoping process, Armorstack assesses your current SIEM deployment against your detection requirements and compliance obligations, and determines the most efficient path to a functional managed program. Sometimes that means leveraging what you have; sometimes it means migrating to a platform better suited to your environment.
What is the difference between managed SIEM and MDR?
Managed SIEM is a component of a full MDR program. MDR (managed detection and response) encompasses the complete security operations function: managed SIEM as the detection engine, plus proactive threat hunting, active incident response, dark web monitoring, and the full analyst team and process infrastructure. Managed SIEM by itself means someone is operating the SIEM platform and monitoring its alerts. MDR means that when those alerts surface a confirmed threat, the provider responds — actively, not just notifying your team. SENTRY delivers both under a single engagement. If your primary need is compliance log retention and alert monitoring, managed SIEM addresses that. If you need the full detection-to-response cycle managed on your behalf, that is the MDR engagement.
How long does SIEM deployment and onboarding take?
SIEM deployment timelines depend on environment complexity, the number of log sources, and the current state of your infrastructure documentation. A well-documented environment with standard log sources — Windows endpoints, cloud workloads, a standard network stack — can be substantially onboarded within the first few weeks of an engagement. Environments with significant OT infrastructure, custom applications, legacy systems, or gaps in asset documentation take longer. The SENTRY 90-Day Proof is designed to get the managed SIEM to an operational and evidence-generating state within the engagement period. Armorstack will give you a specific timeline estimate during the scoped assessment phase, not a generic number that may not reflect your environment.
Can a managed SIEM satisfy HIPAA audit control requirements?
A managed SIEM that continuously collects audit logs from systems containing ePHI, actively monitors those logs for anomalous activity, retains them for the required six-year period, and generates documented evidence of that activity addresses the core requirements of HIPAA’s Audit Controls standard (§ 164.312(b)). HIPAA does not mandate any specific technology. It requires that covered entities and business associates implement mechanisms to record and examine activity in systems containing ePHI — and that those mechanisms are part of a documented security incident response program. SENTRY’s managed SIEM, combined with the SENTRY analyst team and incident response capability, is designed to satisfy these requirements. SENTRY is not a complete HIPAA compliance program — policy, physical safeguards, and workforce training are outside its scope. Armorstack’s VERITY advisory team provides vCISO services that map the complete HIPAA posture.
What happens when the SIEM goes down or a log source stops sending events?
Log source monitoring — detecting when a source goes silent — is a required part of any security operations program. CMMC AU.3.045 explicitly requires alerting when an audit logging process fails. SENTRY’s managed SIEM includes continuous monitoring of log source health: if an endpoint stops sending events, if a firewall stops forwarding logs, or if a cloud connector breaks, the SENTRY team receives an alert and investigates before that gap represents a meaningful coverage hole. This is one of the operational functions that in-house SIEM deployments most frequently overlook — the platform is deployed and operating, but no one is monitoring whether all the expected sources are actually feeding it.
How does managed SIEM pricing work? What drives the cost?
Managed SIEM cost is driven primarily by four factors: the volume of log data ingested (measured in GB per day or events per second, depending on the underlying platform), the number and complexity of log sources requiring onboarding and maintenance, the compliance framework requirements that shape retention duration and evidence packaging, and the level of analyst coverage and response capability included. Organizations with large OT environments, high-volume application logs, or multiple compliance frameworks will have different cost profiles than organizations with standard IT environments under a single framework. Armorstack scopes every SENTRY engagement based on your specific environment — there is no published per-seat rate that accurately reflects what your configuration will cost. The right starting point is a scoped assessment or the 90-Day Proof, which will produce a specific proposal based on your actual environment.
Your SIEM Should Be Working For You. If It’s Not, the Problem Is Operations.
Armorstack SENTRY delivers managed SIEM as the detection engine at the center of a 24/7 security operations program — fully deployed, continuously tuned, and monitored by security professionals who know what they are looking at. Compliance evidence generated as a byproduct of the program, not assembled manually at audit time.