Cheap ones had zero range. My backup sensors turned off automatically after about 5-5 seconds. After troubleshooting I found online by pressing the sonar on/off button multiple times that the code indicated that the right center sensor was faulty. Installed a replacement sensor and the system stayed on thought I had a winner but after checking the range of all the sensors and going to each one I found the originals started beeping about 4ft away but the new one didn't feel me at all, even when I'm completely covered by my hand. After all, the system remains with three more jobs. I will find a better device and replace it.