When it comes to driving, technology is a double-edged sword. On the one hand, features like autobraking, adaptive headlights, electronic stability control, blind spot detection and lane departure warnings have made cars demonstrably safer. Yet other technologies are a mixed bag. Many semi-autonomous vehicle features fall into the latter category.

With the race to make self-driving cars available to the average consumer, forward-thinking auto manufacturers such as Tesla are increasingly incorporating these features. The problem is that consumers tend to overestimate their capabilities.

When drivers put too much faith in their vehicles

This issue was vividly illustrated earlier this week when a Tesla Model S going 65 mph slammed into a parked fire truck on a California freeway. The driver (who was miraculously uninjured) apparently claimed his autopilot was engaged. The system failed to detect the fire truck, and the driver didn’t react in time.

Similarly, another Tesla driver who was arrested on suspicion of DUI claimed he wasn’t actually driving because the car’s autopilot was engaged. His blood alcohol level was twice the legal limit. Needless to say, he isn’t likely to get away with it.

Semi-autonomous is not self-driving

These cases highlight the critical difference between self-driving versus semi-autonomous vehicles. Semi-autonomous technologies such as autopilot simply aren’t designed to replace human judgment. Tesla’s autosteering function, for example, can’t navigate around obstacles. Accordingly, auto manufacturers emphasize that drivers should still remain fully attentive, alert and ready to react during the entire time these systems are engaged.

But drivers aren’t getting the message. Prioritizing convenience over safety, some even go so far as to ignore their vehicle’s built-in warning systems – such as audible alarms that sound when the driver’s hands are off the wheel for too long – which are supposed to keep them alert and engaged.

If you’re considering a vehicle with semi-autonomous features (or are already driving one), be careful. Understand that those systems can backfire. Don’t rely on them to keep you safe. And don’t let their convenience lull you into a false sense of security.