The traffic light was first introduced in 1920 by a police officer named William Potts. He used red, amber and green lights plus 37 dollars worth of wire then hung it up in Detriot.
In 1923 Vladmir Zworykin invented the first picture tube, which later became known as the television. In 1924 he filed for a pateint for the invention.
The first hair dryer came out in the 20's but it was really large and oversized it also overheated frequently. Before it came out women used their vacuum cleaners to dry their hair. they would insurt a hose into the exhaust of the vacuum.
The first video phone was invented in 1925 by Dr. Herbert. He wanted to speed up AT&T's process so much that you could see people's faces so he got a camera and had people try it people would talk and move a rapidly moving beam of light. He presented it to AT&T in 1926 and had the executives talk to each other through the phone they could see each other by a 2 by 2 and 1/2 inch box.
General Electric invented the first flash bulb in 1927. It replaced the dangerous powder that photographers had been using before that.
In 1921 the first lie detector machine was created. John A. Larson who was a medical student at the time invented the polygraph test. The machine was trained to listen to their heart and pulse. Later it was added to watch for sweating if someone started to sweat an alarm would sound and it indicated lying.