642. Cheap Burglar Alarm.—If you can invent an effective burglar alarm which can be sold at ten cents per window, you will have a monopoly in that article.
643. Collapsible Fire Escape.—One which may be folded or rolled and kept beneath the window-sill, and which, when occasion requires, may be extended by throwing the unattached end to the street.
644. Air Tester.—We have a barometer to test the vapor and a thermometer to test the heat. Who will make a contrivance that will test the quantity of pure oxygen in our rooms, and also detect the presence of disease germs? Vast possibilities of wealth and fame open in this direction.
645. Life Boat Launcher.—The two ends of the boat should be attached to the arm of a crane, one chain of which swings the boat clear of the ship, while another releases it from its fastenings. To the inventor this will be Fortunatus’ boat.
646. Saw-Tooth Crutch.—Provide a crutch with teeth on the under side so that it can be used on ice or sleety pavements without slipping.
647. Elevator Safety-Clutch.—Such a clutch has recently been invented, but it acts too suddenly; what is needed is one which in time of accident will bring the elevator to a stop slowly.
648. Gun-Guard.—A rubber guard for guns which will prevent their accidental discharge.
649. Pocket Disinfector.—One has often to go into unhealthy neighborhoods and places where disease germs lurk. A small flat can, filled with some disinfectant which could be conveniently squirted, would be not only a killer of offending odors, but also a saver of life.
650. Automatic Fire Alarm.—Procure some substance easily melted by heat; which, when melted, releases a spring which operates an alarm bell.
651. Key Fastener.—A little thought properly applied will invent a device whereby a key in a door will be proof against a burglar’s nippers, it being impossible to turn the key until the device is removed.