> ## Documentation Index > Fetch the complete documentation index at: https://panaptico.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # System Sensor: Read and Verify Live IT Estate State > System Sensors continuously read your live IT estate field by field, comparing current state against declared targets to produce at-target, off-target, unknown, or unobserved results. System Sensors are Panaptico's always-on readers for your live IT estate. They poll accounts, devices, policies, configurations, and other fields across identity, cloud, network, security, endpoint, and data systems. Each read produces a current state snapshot that Panaptico compares against your declared target. The result is never silently assumed: every field is either at target, off target, unknown, or unobserved. ## How System Sensors work Sensors operate in three acquisition modes depending on the source: * **Ask** — scripted API pulls against providers like Google Cloud, AWS, Okta, or Azure AD. * **Listen** — log, metric, and event streams ingested via Cribl into your data lake. * **Test** — active probes that verify behavior, including negative verification (for example, sending a packet and proving it is dropped). After each read, Panaptico evaluates the field against your declared intent. If a firewall rule should allow only private ranges, the sensor checks `sourceRanges`. If the field is `0.0.0.0/0`, the result is **off target**. If the provider API is unreachable or the field is not returned, the result is **unknown** or **unobserved**. Missing evidence never inherits a last good value and is never manufactured into a pass. ## Result states | State | Meaning | | -------------- | ------------------------------------------------------------------- | | **At target** | Current state matches declared intent. | | **Off target** | Current state diverges from declared intent. | | **Unknown** | The sensor could not read the field, so state cannot be determined. | | **Unobserved** | The field has never been read or the resource is not inventoried. | ## Example: Google Cloud firewall rule You declare that a firewall rule should allow traffic only from private IP ranges. The System Sensor reads the rule and finds `sourceRanges: ["0.0.0.0/0"]`. Panaptico marks the field **off target** and surfaces the gap in the relevant Initiative. When you change the rule to `sourceRanges: ["10.0.0.0/8"]`, the next sensor poll marks it **at target** and closes the gap automatically. ## When to use System Sensors Use System Sensors when you need continuous, field-level verification of configuration state across cloud, identity, network, endpoint, and security systems. They are the foundation for every other Panaptico primitive: Signals, Initiatives, and Routing all depend on sensor reads. Turn raw sensor telemetry into business meaning with scored thresholds and full drift history. Group sensor-verified fields into budget-level programs with gap analysis and closed work loops. See how continuous sensor verification drives system quality and assurance programs.