This paper presents a practical design of backdoor to permanently bypass the screen lock mechanisms on Android devices. Our design has many advantages such as difficulty in detecting backdoor, fast execution time and low power consumption. The key feature of our backdoor is remote triggering that allows the backdoor to be temporarily triggered and executed through push notification services also used by many normal applications. Furthermore, in our proof-of-concept backdoor, about 98% of 4-digit PINs and screen lock patterns were cracked within 5 seconds, and only a small amount of power was consumed. We show the stealthiness of our backdoor to effectively evade the existing malware detection tools (55 anti-virus scanners provided by VirusTotal and SandDroid).