Temperature sensor is a device, to measure the temperature through an electrical signal it requires a thermocouple or RTD (Resistance Temperature Detectors). The thermocouple is prepared by two dissimilar metals which generate the electrical voltage indirectly proportional to change the temperature .

In general,a temperature sensor is a device which is designed specifically to measure the hotness or coldness of an object. LM35 is a precision IC temperature sensor with its output proportional to the temperature (in °C). With LM35,the temperature can be measured more accurately than with a thermistor.

The principle behind this sensor is that of that pure metals change their resistivity with temperature in a predictable way. ... Metals used should a have high boiling point, be easily available in its pure form, be resistant to corrosion (chemical stability) and have electrical properties that are highly reproducible.

Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation . Though its reading of peripheral oxygen saturation (SpO 2 ) is not always identical to the more desirable reading of arterial oxygen saturation (SaO 2 ) from arterial blood gas analysis, the two are correlated well enough that the safe, convenient, noninvasive, inexpensive pulse oximetry method is valuable for measuring oxygen saturation in clinical use.

Principles of pulse oximetry Oximeters work by the principles of spectrophotometry: the relative absorption of red (absorbed by deoxygenated blood) and infrared (absorbed by oxygenated blood) light of the systolic component of the absorption waveform correlates to arterial blood oxygen saturations.

The pulse oximeter works out the oxygen saturation by comparing how much red light and infra red light is absorbed by the blood. Depending on the amounts of oxy Hb and deoxy Hb present, the ratio of the amount of red light absorbed compared to the amount of infrared light absorbed changes.

Heart beat sensor is designed to give digital output of heat beat when a finger is placed on it. When the heart beat detector is working, the beat LED flashes in unison with each heart beat . This digital output can be connected to microcontroller directly to measure the Beats Per Minute (BPM) rate.

The heartbeat sensor is based on the principle of photoplethysmography. It measures the change in volume of blood through any organ of the body which causes a change in the light intensity through that organ (avascular region). ... Reflection: Light emitted from the light-emitting device is reflected by the regions.

A gas sensor is a device which detects the presence or concentration of gases in the atmosphere. Based on the concentration of the gas the sensor produces a corresponding potential difference by changing the resistance of the material inside the sensor , which can be measured as output voltage. 

Gas sensors (also known as gas detectors) are electronic devices that detect and identify different types of gasses. They are commonly used to detect toxic or explosive gasses and measure gas concentration.

MOS sensors detect concentration of various types of gases by measuring the resistance change of the metal oxide due to adsorption of gases. Atmospheric oxygen residing on the MOS surface is reduced by the target gases, allowing more electrons in the conduction band of the metal oxide material.

Therefore, by using this sensor it is possible to detect the exhaled air from human body is wether or not the user have cougn or COVID-19 based on the content of echaled air gas from body.

Blood pressure measurement
The non-invasive auscultatory and oscillometric measurements are simpler and quicker than invasive measurements, require less expertise, have virtually no complications, are less unpleasant and less painful for the patient.

However, non-invasive methods may yield somewhat lower accuracy and small systematic differences in numerical results.Non-invasive measurement methods are more commonly used for routine examinations and monitoring. New non-invasive and continuous technologies based on the CNAP vascular unloading technique, are making non-invasive measurement of blood pressure and further advanced hemodynamic parameters more applicable in general anesthesia and surgery where periods of hypotension might be missed by intermittent measurements