It will change color & come off with a slight tug. Don't pick it early! Just leave it on there & if you forget, it will fall off- But that's fine. I had one fall & I thought I lost it.. Was rather angry as it was a cross... But I found it again 3 weeks later & it was fine.

some varieties fall off the vine when green and then ripen indoors. They'll gor brown then purple and start wrinkling. The more purple the better and the more wrinkled the better - that's when they are ripe.