sensors
Thermistor: Low Cost and Fast Response Time.
Characteristics of thermistors include a moderate temperature range of -55° to 125°C (though some are capable of much higher temperatures), low-to-moderate cost (depending on accuracy), and fast response time.
The semiconductor thermistor is usually made up of small beads of complex materials such as cobalt, nickel, iron, zinc and glass, the resistance of which is very temperature dependent.
Thermistors are used inside many devices as temperature sensing and correction devices as well as in specialty temperature sensing probes for commerce, science and industry including in the new digital thermometers used in medicine.
pulse oximeter
Pulse oximetry estimates arterial oxygen saturation by measuring the absorption of light of two wavelengths (approximately 660 nm and 940 nm) in human tissue beds. The amount of light absorption varies with the amount of blood in the tissue bed and the relative amounts of oxygenated and deoxygenated haemoglobin. The accuracy of commercially available oximeters differ widely, probably due to the algorithm differences in signal processing.
And to minimize the cost pulse oximeter also used to measure blood pressure and heart beat.
The SpO2 (peripheral capillary oxygen saturation) sensor uses two emitting LED’s one in the red region and the other in the infrared region of the spectrum. The reflected light of each one of these LED’s is absorbed by a photodiode that converts this current into a digital value that is sent via SPI. This sensor can be used to estimate the oxygen saturation level on the blood with +/- 2% accuracy compared to a medical sensor.
Gas sensor: MQ-135
Microcontroller
Arduino is an open-source platform used for building electronics projects. 
Arduino consists of both a physical programmable circuit board (often referred to as a microcontroller) and a piece of software, or IDE (Integrated Development Environment) that runs on our computer, used to write and upload computer code to the physical board
Arduino is used to control all the sensors.
There are two main parts every sketch will always have;
Void setup ():- this is the first routine that begins when the Arduino starts functioning. This function is executed only once throughout the entire program functioning.
Void loop ():-this is the next important function in the sketch. It consists of that part of the code that need to be continuously executed unlike the part of the code written in the set up function.
A printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. Printers vary in size, speed, sophistication, and cost.
Resistor
Electrical component that transmits current in direct proportion to the voltage across it
Capacitor
Capable of storing an electrical charge; especially one consisting of two conductors separated by dielectric.
Transistor
Solid state semiconductor device with three terminals, which can be used for amplification, switching, voltage stabilization, signal modulation, and many other functions.
Transformer
A static device that transfers electric energy from one circuit to another by magnetic coupling. Their main use is to transfer energy between different voltage levels, which allows choosing most appropriate voltage for power generation, transmission and distribution separate.
Wire
The purpose of the wires in a series circuit is to allow the electricity to flow from one device to the next. Wire is used to carry the flow of electrons. Metal wire is a very good conductor. Materials that do not allow electricity to flow through are called insulators or non-conductor