Background: The majority of dogs with idiopathic epilepsy continue to have seizures despite appropriate treatment.Objectives: To assess the use of a commercially available, collar-mounted accelerometer to detect generalized seizures in dogs.Animals: Twenty two client-owned dogs with idiopathic epilepsy.Methods: Six-month prospective clinical study during which dogs wore a collarmounted accelerometer. Seizure documentation was based on owner observations and video recordings. The accelerometer used a predefined algorithm to detect seizures in the first study phase, and an individualized algorithm in the second study phase. Caregivers completed a quality of life (QoL) questionnaire at the initial and final study visit.Results: Using the predefined algorithm, the accelerometer detected seizures with a sensitivity of 18.6% (95% CI [13.4%, 23.8%]) and mean false detection rate of 0.096/ day. Values did not change significantly with use of an individualized algorithm (sensitivity 22.1%, 95% CI [15.1%, 29.0%]; false detection rate 0.054/day). Mean composite QoL score was significantly improved at study completion (50.42) compared to study initiation (39.53; P = .005), and this change was moderately correlated with a change in weekly exercise (r = 0.46, P = .05).Conclusions and Clinical Importance: Generalized seizures in dogs can be detected with a collar-mounted accelerometer, but the overall sensitivity is low. K E Y W O R D S activity monitor, canine, clinical trial, idiopathic epilepsy