Does an holter montior detect cardiac arrythmias?

Yes: Yes, a holter will detect an arrhythmia only if you have the arrhythmia during the monitoring period (while wearing it). Sometimes people need a longer term monitor or event monitor to catch a rhythm problem.

Holter monitor: Yes, but even better are monitors that you can wear for 2 - 4 weeks as they may pick up arrhythmias that may not show in a 24hr holter.