Yes, there are ways of making more secure hand scanners. The article links to the exact model, if you're interested. No, it probably isn't perfect. But it's part of a larger security system; remember, whatever you're bringing to "hack" this door, you must have also slipped past a physical inspection. I don't necessarily expect total brilliance from the security guards, but I suspect they would know enough to ask you some very pointed questions if you tried to sneak in a to-scale replica of somebody's hand.