Biometric devices are honest to a fault. Linger near the reader for a few seconds and it records the same person arriving three times. Multiply that by a few hundred employees and the attendance data is technically real and practically unusable.
The sync layer decides what counts as one event: punches under 60 seconds apart collapse into a single record. Each employee's timezone is resolved before the date is taken, so a punch near midnight lands on the right day. The sync watermark only advances when the fetched window actually moves past it, and every record keeps its provenance — device import or manual entry.
HR notifications moved from email to WhatsApp: check-ins, absences, expiring documents. That's where the second lesson came from. A historical resync once fired hundreds of messages about attendance that was months old.
Now there's a circuit breaker, and stale events are skipped rather than announced. It's a small rule that exists because we saw the failure — which is the best reason to write one.
The result is attendance data the payroll engine can actually trust.
Read the case study: Biometric attendance data the payroll engine can trust