Against the emergence of "the Internet of Bodies," Christopher O'Neill presents an incisive long history of biosensing technologies from the mid-nineteenth century to the present. As O'Neill shows, sensor technologies work by failing—if their mode of measure never quite captures the body, this is a feature and not a bug. Nobody and no body really fits into the Internet of Bodies, but the endless correction of biosensor errors works to endlessly extend the reach of the sensor society.   O'Neill's book traces the emergence and transformation of the cultural techniques of biosensing which "work through" these errors, examining how the early pulse-writing sensors of the sphygmograph produced a newly educated touch in the medical clinic; the way work measurement technologies not only optimized but introduced a new intimacy into the post-Fordist workplace; and how the sensors in nineteenth-century burglar alarms enabled a new choreography of servants' movements in the American home. These histories, as O'Neill demonstrates, presage contemporary anxieties surrounding the Quantified Self movement, the management of affective intensities in digitally surveilled workplaces, and the integration of the gig economy within the smart home.   Just as O'Neill demonstrates that technologists' claims to objectivity, transcendence, and omniscience remain frustrated by the messy reality of the body, the book also shows that we must go beyond the typical critical gesture of pointing out errors, biases, and false assumptions about the body, and instead show what precisely these errors do.