In this paper we present a wearable assistive technology for the freezing of gait (FOG) symptom in patients with Parkinson's disease (PD), with emphasis on subjective user appreciation. Patients with advanced PD often suffer from FOG, which is a sudden and transient inability to move. It often causes falls, interferes with daily activities and significantly impairs quality of life. Because gait deficits in PD patients are often resistant to pharmacologic treatment, effective nonpharmacologic treatments are of special interest. We have developed an ambulatory device that detects FOG episodes in real-time and provides an automatic cueing sound until the subject resumes walking. We tested our device on ten PD patients. Eight patients experienced FOG during our study. Over 8h of data has been recorded and 237 FOG events have been identified by professional physiotherapists in a post-hoc video analysis. The device detected the FOG events with a sensitivity of 73.1% and a specificity of 81.6% on a 0.5 sec frame based evaluation. The most important finding of the study is that we can provide online assistive feedback for FOG events in PD patients. Based on subjective reports, the majority of patients indicated that the context aware automatic cueing is beneficial for them.