There are plenty of sensors in a smartwatch and one of the most common ones is PPG or Photoplethysmography.

It works by shining a LED light into the skin and measuring the changes in blood flow with each heartbeat. The smartwatch then uses an algorithm to calculate how many times the heart beats each minute.Some smartwatches also use a different type of sensor, ECG or Electrocardiography. These are more accurate than PPG sensors. It measures the electrical activity of your heart to calculate the heart rate. Many smartwatches use a combination of PPG and ECG to improve accuracy.

Smartwatches often use a combination of different sensors depending on the scenario to track steps and activities.

Generally, it uses a combination of accelerometers to detect changes in motion such as steps taken, distance traveled and calories burned. GPS is used to track outdoor activities including running, walking, and cycling. It is also used to provide more accurate distance and speed data.

Most smartwatches after syncing with your phone are able to make calls and send texts by using the internet. Your smartwatch needs to be connected to your phone either through Bluetooth or through a mobile network. You need to have a dialer and message app on your smartwatch. Smartwatches with built-in cellular or LTE connectivity work standalone and can be used to dial due to inherent cellular connectivity.

Yes, smartwatches are perfectly safe. In fact, they are a great companion device for your smartphone and a nifty health tracking device that can tell you crucial information about your health vitals including heart rate, BP, calories, and more.

Generally, the data related to your activities such as the steps you walked are more or less accurate. However, with more complex data where your smartwatch needs to be extrapolated, then it becomes a little dicey. For instance, it is known that the calories burned counter is not really accurate. Some are more inaccurate than others.Other health-related data such as sleep cycles are also accurate only to a certain degree.

The same goes for heart rate and blood pressure monitoring. These are still not reliable and accurate to the point that they can be used for a clinical diagnosis. Having said that, it is still a great companion device to give you an estimate of trends in relation to your health and body rather than accurate statistics.

Yes, you can use both a non-cellular as well as cellular smartwatch without a smartphone. But there are caveats that need to be aware of. Firstly, most of the features on a smartwatch are functional as long as it is connected to a stable Internet source.You need to connect to the source of Wi-Fi or you need to have built-in cellular connectivity to function independently of a phone. For this, you should have a separate smartwatch data plan.