This observational study compared three methods for measuring community first responder (CFR) arrival times in a smartphone alerting system (SAS) for out-of-hospital cardiac arrest: GPS entry into a 100m radius (GPS100m), GPS entry into a 50m radius (GPS50m), and manual in-app confirmation — across 1,498 alerts over 12 months in Freiburg, Germany.
Median arrival times differed significantly across all three methods (p<0.001): GPS100m = 4:21 min, GPS50m = 4:40 min, and manual confirmation = 5:50 min; manual confirmation was absent or delayed in 30.8% of cases, while GPS50m showed the smallest bias on Bland-Altman analysis.
Single-system, single-region study (Freiburg, Germany), limiting generalizability to other SAS platforms or geographies; manual confirmation served as a comparison reference but is itself unreliable (missing in ~31% of cases); GPS accuracy may be affected by urban environments or device variability.
When evaluating or optimizing smartphone alerting systems for cardiac arrest response, use GPS-based 50m geofencing as the standard arrival metric — it is objective, nearly always captured, and more consistent than manual app confirmation.
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