Instructions
Lockpicking
Purchase, find or steal a lockpick and a probe. Regular stores don't sell these items, but you can buy them from underground markets if you're a Thieves Guild member. Lockpick quality ranges from Apprentice to Grandmaster. Lower-quality picks and probes break more often.
Face a locked door to see the lock level. If the level is low, such as 10, an Apprentice pick will open it. High-level locks, such as 80 and above, need a Master or Grandmaster pick. When facing a door, a message will display if the door is trapped.
Equip a probe if the door is trapped. Press the ̶0;Attack̶1; button to disarm the trap.
Equip a lockpick and press the ̶0;Attack̶1; button to use it. If the picking works, the door opens. If you see the message ̶0;Lock too complex,̶1; your Security level is too low or the pick's quality is too low for the lock's level.
Open Spell
Buy an Open spell from an Alteration magic trainer. The most basic spell is Ondusi's Open Door, which unlocks doors up to level 50. Trainers sell this spell in the Balmora, Vivec and Ald'ruhn Guild of Mages.
Equip the Open spell and stand in front of a locked door.
Press the ̶0;Attack̶1; button to cast the spell and open the door. You might need to cast the spell several times to unlock the door.