Introduction

Various sensors have been developed for detection of arousal, usually referred to as edging sensors.

Anal pressure-based sensor

Originally developed by Bohlen in 1979, consists of an inflatable buttplug attached to a pressure sensor. This type of sensor is used in the nogasm and clones, later commercialized by Maus-Tec into the Edge-o-Matic 3000.

Depending on the exact shape of the plug, either the internal anal sphincter or external anal sphincter is measured.

Two main design approaches exist, the inflatable buttplug type and the coiled tube type.

inflatable buttplug type: https://github.com/diglet48/toy-designs/tree/main/inflatable%20buttplug%20pressure%20sensor
coiled tube type: https://github.com/diglet48/toy-designs/tree/main/large%20flo%20pressure%20sensor

The main problem with pressure-based sensor is that they leak. Due to the permeability of the tubing, the coiled tube type leaks at a rate that makes it unsuitable for play.

Girth sensor

A girth sensor measures penile diameter / circumference.

It can measure erect state as well as activity from the ischiocavernosus muscle. The other muscles in the pelvic floor don't seem to contribute much to erection (Shafik 1995)

diglet developed a non-intrusive sensor: https://github.com/diglet48/toy-designs/tree/main/omega%20clamp

EMG sensor

EMG, or electromyography, is a technique for measuring muscle activity by observing their electrical activity.

Normal metal buttplugs or sticky pads can be used as electrodes. With metal buttplugs, the main muscles that are measured are the internal and/or external anal sphincter. With sticky pads, the bulbospongiosus muscle can be measured. Literature generally utilizes needle electrodes for precise targeting.

Heart rate sensors

The data from heart rate sensors does not appear to well-correlated with edging behavior.

Galvanic skin response (GSR) / Electrodermal activity (EDA)

The data from GSR/EDA does not appear to be well-correlated with edging behavior.

Photoplethysmogram (PPG)

Needs research. Could be used for girth measurement.

references:

Shafik 1995: response of the urethral and intracorporeal pressures to cavernosus muscle stimulation: role of the muscles in erection and ejaculation
Bohlen 1979: An Anal Probe for Monitoring Vascular and Muscular Events During Sexual Response