How to tell if mortice lock on door is exterior or interior?

I'm trying to picture the lock you're describing. I have mortise locks on every door in my house, and they all have doorknobs too. (I suppose a doorknob could be considered a handle)

My mortise locks aren't considered interior or exterior. They all can lock from either side with a skeleton key. The actual locking mechanism inserts into the door itself & then the knobs go through the door.

Here's an example of one made like mine. Is this what yours looks like?

http://www.google.com/imgres?imgurl=http://img1.et...

Edit to add: I believe the locking mechanism itself is a bit beefier on an exterior mortise lock, but on my place...the same key locks my driveway door, my back door and every interior door.

Mortice locks come with a variety of levers. The higher the number the more complicated and therefore secure lock. It is common for internal doors (bathrooms and bedrooms) just to have 3 levers locks whereas an external door would have a 5 or 7 lever lock. If you look at the plate on the side of the door next to the keyhole - where the case of the lock fits in to the door - it should say what lever the lock is. You should also check with your house insurance as to what level of security is required. In the UK most insurers require a minimum of 7 lever.

A few pics would help answer your question. They have been making mortice locks for hundreds of years and there are many different types. In general the interior one's had simple keys with just a couple teeth (skeleton-keys). Just for your own safety I'd have a lock smith look at your exterior locks and make sure they are safe. If not you can install dead bult locks above them, or buy better quality mortice locks for the exit doors.

as most answers say ..an interior mortice has a simple key ...if you have an external 5 lever mortice lock ,,apart from a more elaborate key and lock mechanism ..the body of lock is often wider as exterior doors are allways wider than an interior door ..the interior locks are very slim ...fit an exterior lock on an interior door and you will have wafer thin sides

You've got it figured right. All the interior morticed locksets have very simple keys. The main house door usually the front....on the older homes.....had a different key. Usually a bit heavier and more teeth. One way to know for sure is to see the original door this lockset came out of....otherwise I believe you have the exterior.

It depends. In case you have the historic-fashioned mortise locks (the lock is a rectangular box set into a pocket in the fringe of the door, has a traditional formed keyhole) altering simply the knob is convenient. They're held onto the spindle via a easy set screw. Simply loosen the screw and twist the knob counter-clockwise to get rid of it from the threaded spindle. You probably have the extra modern cylindrical locks, it's a topic of getting rid of four screws. Two maintain the latch in the fringe of the door, two hold the two halves preserve the lock together in a 2 1/8 inch hole through the door. Also handy. When you imply that you wish to have to replace mortise locks with today's ones, do not try it should you don't seem to be real helpful. There are conversion kits to be had, but they contain way an excessive amount of reducing and chiseling for an novice.

all the exterior mortice locks I have ever seen have two buttons on the face near the catch that allows you to either lock or unlock the catch by pressing one or the other buttons and uses a regular shaped key, the ones that use a skeleton key are the interior ones

exterior ones look like this; http://www.google.com/imgres?imgurl=http://locksmi...