Before rushing out to buy an alarm, try to determine what you want a system to do for you. Morgans are rarely stolen. The statistics in Canada indicate one theft nationwide in ten years. Morgans are easy to track and it takes too long to find buyers for the parts. That being said they may still be the target for rowdy youngsters looking for a joy ride. The greatest danger is losing something from the car..a purse, a camera, or even worse..vandalism. Morgans draw attention like bees to honey and with that attention comes dangers from inquiring fingers looking for a souvenir or wishing to leave a memento on your clearcoat.

I have been told that if car theft was a company, it would rank  number 40th on Fortune's 500 biggest companies in the world. I don't know if Morgans contribute much to this positioning.
 

THEFT OF THE CAR

If you just want to prevent the theft of the car that are some ancient remedies and some new ones. You can remove a vital part such as the ignition wire betwen the coil and the distributer and I have even heard of those who take the steering wheel with them. An ingeneous method is to immobilize the car with the safety brake. Simply pull the lever as reasonably tight as you can and then screw off the chrome release button and take it with you in your pocket.

Alternatively you can an ignition interrupter..a device that interrupts the ignition unless you flash the head lights or utrn on the radio before turning the key.

THEFT FROM THE CAR AND VANDALISM

We travel a lot with the Morgan and often we have to park in interesting areas. As has been noted, it is difficult and tedious to find a safe place for everything and toting around a laptop, cameras and  assorted valuables is not fun when you want to do some quick window shopping or have a glass of something.  Also...though hotels are often very kind to Morgan owners, the car is still left out of sight for a  night occasionally and Morgans do draw attention and strange hands.

After putting up with these worries for years, on a whim I purchased an alarm system while shopping for something else. It was not expensive and I did the installation myself. There is an excellent area to place it  (excellent for the pre-2000s) in the rear on the other side from the battery and it can be attached easily directly onto the rear wood panel of that is the sloping cabin wall. The power connection can be made right onto the battery two feet away and the wires tacked to the wall or tie-wrapped out of the way.

There is a "armed" light and though it is optional it is a good idea because you want it to be visible to passersby. I ran the wires under the carpet and then behind the dash and finally ran it through the  dash for the 1/8 inch light.

The alarm has motion, proximity and ignition detectors. That means if someone leans into the car (even without touching it) or touches it (with as little or as much degree of force YOU have programmed as "too" much) or if anyone tries to start the car...the alarm goes off. Bingo! you have made the whole car safe and without needing to hide anything. It operates by a remote and can be turned off or on  from quite some distance (50+ meters).

We discovered a hidden bonus was after it was installed. When we mentioned the installation to our insurance broker, the insurance company paid for 75% of the cost and lowered our premiums 10% yearly! Not a bad 50 USD investment.

Some sources

Commando  (Starts at 69 USD)
Auto Barn (Alarms and anti-theft devices)
Car Radio Alarms

AN ADDENDUM
from Stephanm Matthaei

I have an alarm as well, the only issue being that, unlike regular cars, one can disconnect the battery of a Morgan from the outside (actually from underneath) without any trouble. No battery, no alarm!

This is why my alarm is powered via a small backup battery underneath the seats. The box and a separate piezo horn are at the same place, because one can also easily disconnect the horn (or the box itself if mounted outside the area protected by the motion sensor).

Finally you can secure your spare wheel and the luggage rack (and anything locked to the luggage rack) by mounting a switch underneath the spare wheel center bolt. If somebody tries to unscrew the bolt  the switch closes and the alarm starts.