The Celkon A21 is a 2014 Android 4.2.2 smartphone powered by the Mediatek MT6582 (28 nm) with 256MB and 512MB internal storage. It features a 4.0", TFT, 320.0x480.0 display and is available in Black, Blue, Red.

The A21 is equipped with a Li-Ion 1500 mAh battery, a 15 MP, Yes main camera, a 3 MP front camera. The device uses a Dual SIM (Dual stand-by) configuration. It weighs 115.3 g.

A bootloop on the Celkon A21 occurs when the device repeatedly restarts without fully loading Android. This is commonly caused by a failed software update, corrupted system files, or an incompatible app. Most bootloops can be resolved without losing data by clearing the cache partition first before attempting a factory reset.

Factory reset may be needed as a last resort — erases all data.