Storm Door locks used to be only available in a couple of variations made by basically the same company but nowadays there is a whole range of new door locks to choose from. All the way from inexpensive to very expensive. Many of these locks can be retrofitted to old storm doors but a few of them require too many modifications to your old door to make it worthwhile.
If your storm door locks are broken, more than likely you can replace it with a model of similar design without too many problems. The first thing to bear in mind is that storm doors come in different thicknesses, and so the screws that hold the lock to the door handle vary in length from door to door. Most new locks come with either different lengths of screws or screws that can be broken off easily to different lengths. Often though the stock screws are still either too long or not long enough so be prepared to go hunting for new screws.
Its also a good idea to replace the handle and the lock together on your old storm door. If you keep the old handle, even if you bought a new lock from the same manufacturer, they frequently change the diameter of the mounting screws. So you may not be able to get the two pieces to join together without stripping the threads in the old handle.
Sometimes when you get the new lock installed, it still wont want to latch properly. Usually you will have to raise or lower the latch plate that mounts on the door jamb to get things working properly. The lock kit often comes with a new latch plate and several plastic spacers to help you get this adjustment right. Sometimes if your storm door was not quite as wide as your wooden door opening, you will need to build a custom spacer block behind the latch. plate.
Another problem that arises when you are installing your own storm door is the existing door knob on the door you are covering with the storm door. The lock on the storm door can often get in the way of the existing door knob. If you buy a new storm door look for model that does not have holes pre-drilled for locks. That way you can locate the lock slightly above or below the level of the existing door knob so they do not bang into each other.
Many of the newer storm doors use more expensive solid brass mortise locks. The dimensions of the locks are unique to their manufacturers so you pretty much need the exact same lock if you want to replace an old non functioning one. Fitting a new mortise lock to an old storm door means you will have to cut accurate rectangular holes in the storm door frame which is pretty difficult. At the factory these holes are punched out with special equipment.