Murdoch Mysteries Wiki

The Pneumograph or Truthizer as named by George Crabtree was created by William Murdoch using the known principles of the pneumatograph or spirograph, a device that records the velocity and force of thorax movements during respiration. Murdoch calls it an Autonomic Response Indicator (ep.1003)

Murdoch explains in his demonstration (ep.108) to the constables of Station House No. 4, "Panic has many signatures– shortness of breath, a rise in blood pressure, stiffening of the limbs. If human physiology changes under duress, then why not use this to our advantage?"

It measures physiological change associated with duress. The machine is connected to a person and measures that person's heart rate and breathing while they are asked a series of questions. Variations in their biometrics cause fluid to rise in a tube on the device. This is generally an indication that the subject is lying.

After calling the lie detector a "Frankenstein contraption" and "your "new mograph' thingy...", Inspector Brackenreid confesses, "Well, I've got one of those at home. It's called a wife."

Appearances and Mentions

Still Waters

  • While still strapped to the Pneumograph and Dr. Ogden is present, Higgins asks him "Is the Detective is in love?" He is saved by the whistle and George reassures him with, "I don't think anybody noticed that, Sir, with you and her and the liquid."
  • Murdoch used his Pneumograph to interrogate James Pearson and Wallace Driscoll of the King's Rowing Club during his investigation into the murder of Richard Hartley.

Invention Convention

  • Murdoch discovers Crabtree demonstrating his devise at the convention, calling it The Truthizer, "Before you say it, sir, I think that your invention simply must see the light of day."
  • "They are not inventions, George. They are simply re-workings of existing technology." Murdoch tries to explain how he holds his creations.
  • George is convinced that the Truthizer might win the Eaton Prize for most commercially promising invention.

A Study in Pink

  • Murdoch has upgraded his Pneumograph with a blood pressure cuff.


  • Historically, a device called the polygraph was invented in 1921 using pneumographic sensors.


Murdoch Mysteries Seasons
Season 1Season 2Season 3Season 4Season 5Season 6Season 7Season 8Season 9Season 10Season 11Season 12Season 13Season 14