However, if your Lock spell's magnitude is lower, the lock will not change. If you cast Lock on an already-locked object, and your spell's magnitude is higher than the lock's current level, the lock's level will change to your spell's magnitude.It is possible to become permanently stuck by locking a door which you cannot unlock.You can lock almost any container, including sacks and barrels.Containers or doors that you Lock and unlock will permanently carry the "unlocked" notice on them.Thus you should try to do this only where there are no potential witnesses (other than followers, who don't seem to mind). Note that lockpicking an owned container or door is considered a crime, even on a container that is not locked by default. You can also use it to practice your Security skill by repeatedly locking and picking the same lock.
The spell you can purchase, Fenrick's Doorjam, costs the minimum of magicka and should therefore be the only Lock spell you ever need. Since NPCs are incapable of picking locks and never cast Open spells, a very weak Lock spell (even 1 point) is just as effective as a stronger one for this purpose, and much easier to cast. This is only applicable on interior doors, not doors which go into a different cell, as NPCs in Morrowind are incapable of using doors which go into a different cell anyway (unless they are following you, in which case they come with you immediately and can't be locked out, and in any case will not attack you). You can bury it or simply throw it in a trash container. Before closing the jar you can say: Seal the jar tightly and take it to a place far away from your home. You can use Lock to trap pursuers or to keep out potential witnesses from a room if you plan to commit a crime there (theft or murder). Inflicts Shadow damage to all enemies within 10 yards of the target. Add 9 drops of vinegar and keep visualizing how the person is removed from your life.You can cast Fenrick's Doorjam (Magicka:1) repeatedly to increase your Alteration ability - a container is not required for success and/or skill improvement. There are few practical uses for this spell effect.The effect is permament until an Open spell is cast on it, or it is picked or opened with a key.