Older and younger drivers' responses to different forward-collision warning systems and their subjective evaluations were studied in a simulated driving task. The systems differed in the settings of the warning threshold and the visibility of possible causes for false alarms. The analysis of mean driving speeds allowed us to assess participants' reliance on and compliance with the systems. Older drivers drove consistently slower, but the patterns of results for both age groups were similar: Reliance (i.e. speed when no warning was given) was greater with systems featuring more false alarms and fewer omissions. Compliance (i.e. the deceleration after a warning) was greater with systems featuring fewer false alarms and more omissions. The ability to see the causes of false alarms led older drivers to express greater subjective tolerance for false alarms. Implications of these results for the understanding of responses to warning systems in general and in-vehicle collision warnings in particular are discussed.