If the Smart Key does not operate normally, you can lock or unlock the door by using the mechanical key.

Press and hold the release button (1) and remove the mechanical key (2). Insert the mechanical key in to the key hole on the door.
To reinstall the mechanical key, put the key into the hole and push it until a click sound is heard.
Start-up
Loss of a smart keyHyundai Tucson (LM) 2010-2015 Service Manual: Valve Body Repair procedures
Removal
1.
Remove the air duct.
(Refer to Engine Mechanical System - "Air cleaner")
2.
Remove the battery and the battery tray.
(Refer to Engine Electrical System - "Battery")
3.
Remove the under cover (A).
Tightening torque :
19.6 ~ 24.5 N.m (2.0 ~ 2.5 kgf.m, 14.5 ~ 18.1 lb-ft) ...
Hyundai Tucson (LM) 2010-2015 Service Manual: Description and Operation
Description
The immobilizer system will disable the vehicle unless the
proper ignition key is used, in addition to the currently available
anti-theft systems such as car alarms, the immobilizer system aims to
drastically reduce the rate of auto theft.
1.
Encrypted SMARTRA type immobilizer ...