QR Code Participant Check-In with n8n, Google Sheets & Slack

Instant QR check-in that logs attendance to Google Sheets—and prevents duplicate scans

This n8n workflow turns a QR code into a fast participant check-in kiosk. It records attendance in Google Sheets, stops the same person from scanning twice using an n8n Data Table, calculates progress toward a required attendance threshold, and sends Slack alerts when certification becomes mathematically unreachable.

What this workflow does

• QR-driven submission via n8n Form: Participants enter their email while the session code is automatically prefilled from the QR link.
• Normalize + build a composite check-in key: The workflow normalizes the email, reads workflow settings (Sheet ID, tab names, Slack channel, threshold), and combines email + session code into a unique key.
• Deduplicate with n8n Data Table: Before logging, it checks the Data Table for the composite key. If it already exists, the participant sees an “Already checked in” completion screen and no duplicate is recorded.
• Log to Google Sheets: For first-time scans, it looks up the participant in a Google Sheets roster and appends a timestamped check-in to the Check-Ins tab. Unregistered attendees are tagged as WALK_IN.
• Track progress and compute attendance %: It reads required sessions from a schedule tab, pulls historical check-ins from the Data Table, and calculates both current and best-case attendance percentages against the threshold.
• Slack at-risk alert + participant confirmation: If the threshold is unreachable even with perfect future attendance, it posts an at-risk alert to a Slack channel, then shows the participant a completion screen.

Use cases

• Training cohorts that require a minimum attendance percentage for certification.
• Event staff want QR kiosk check-in with automatic walk-in detection.
• Organizations need duplicate scan prevention and real-time coordinator notifications.

Technical details

• n8n nodes: if, set, code, form, slack, data table
• Integrations: n8n Form (check-in submission), Google Sheets (roster, Check-Ins, schedule), Slack (at-risk alerts)
• Core logic: composite key (email + session code) + Data Table deduplication + threshold reachability calculation