# ADR-005: Device Status Calculation

## Status
Accepted

## Context
Devices report heartbeats at regular intervals. We need to determine online/offline status.

## Decision
- Agent sends heartbeats every 30 seconds (configurable)
- Server marks device as `online` on each received heartbeat
- A background worker checks for stale devices every 60 seconds
- If last heartbeat is older than 2 minutes, device is marked `offline`
- If metrics show concerning values (disk > 90%), device is marked `warning`

## Rationale
- Simple threshold-based status is reliable and easy to understand
- Status transitions are logged for audit purposes
- The threshold is configurable per-device or globally
- Future: more sophisticated health scoring

## Consequences
- Status is computed server-side, not trusted from the agent
- The heartbeat interval affects status responsiveness
- Status changes generate audit events and can trigger alerts