Why Single-Metric Alerts Fail
Standard Garmin alerts watch one number at a time. Power creeps up a little, heart rate drifts up a little — neither triggers an alert alone, but together you're quietly cooking yourself. By the time one metric finally crosses the line, you've been overcooked for minutes.
The Problem
Single-metric alerts miss the compound effect. Power at 95% of threshold plus HR at 95% of threshold equals a rider heading for a bonk — but no alert fires.
The Solution
Z2 Training Monitor watches power and heart rate together. When both approach their limits simultaneously, it triggers a combined alert — even if neither has individually crossed the threshold.
Key Features
Everything you need for intelligent zone 2 training on the Edge 840
Four-Row Display
Instant power, 30-second normalized power, heart rate, cadence, and distance — all visible at a glance with high-visibility typography
Two-Stage Alerts
Inverse video when approaching thresholds, flashing at ~0.5 Hz when exceeded — progressive urgency without taking your eyes off the trail
Dual-Threshold Detection
When both power and heart rate breach warning levels simultaneously, both tiles flash — catching quietly overcooked efforts that single-metric alerts miss
Bonk Detection
Dedicated alert triggers when power drops below Z2 floor for 60+ consecutive seconds while HR is also declining — the telltale sign of fatigue
Fully Configurable
All eight thresholds are user-adjustable through Garmin settings — power, HR, normalized power, bonk threshold, and alert delay — no recompile needed
Normalized Power
30-second rolling average smooths out power spikes from terrain changes, giving you a true picture of sustained effort
How the Alert System Works
Three layers of protection keep you in zone 2
- Warning stage — tile background inverts when approaching threshold (e.g., power nearing limit)
- Alert stage — tile flashes at ~0.5 Hz when threshold is exceeded
- Combined alert — if both power AND heart rate are in warning simultaneously, both tiles flash even though neither has individually crossed the alert threshold
- Bonk alert — power stays below Z2 floor for 60+ seconds while HR declines, signaling fatigue onset
- All thresholds configurable per-rider through Garmin Connect IQ settings
- Alert delay prevents false positives from brief spikes during technical sections
Technical Details
Built With
- Monkey C (Garmin Connect IQ SDK)
- Connect IQ Data Field API
- 30-second rolling normalized power
- Configurable threshold engine
Requirements
- Garmin Edge 840 (or compatible)
- Connect IQ 4.x+
- Power meter (ANT+ or Bluetooth)
- Heart rate monitor