Most tech companies supervises multiple testing techniques in their process of hiring a candidate for a technical role. Typically 2-3 steps lay ahead a candidate when they are going through hiring procedure in such companies. The hiring process takes at least 30 days to get complete depending on the hiring team.
You may have come across several companies who offer job via a phone interview only, but there are other companies who prefer to go with a thorough hiring procedure before handing the job offer to a candidate. Those companies use multiple steps to evaluate if a candidate is right for the company. They place various interviews strategically, one after another in the process of hiring.
In a technical company, the first interview is usually taken by a technical recruiter but not an engineer. This recruiter will evaluate first whether what you do can provide any positive impact on the company and it is in alignment with the job opening present at the company at that time. It is challenging for the recruiter to choose a candidate for the next interview without being an engineer himself/herself.
The level of the first interview is way higher than the others as it is your first interaction with the recruiter. The recruiter doesn't want to know about your technical skills at all but will ask questions that are thoroughly conceptual. Your basic understanding can make your way to the next interview in the hiring procedure of the company.
In the second round, you have to give a technical interview via a phone call, or you may have to come in a video call. A pro will take this interview. He/she will have the in-depth technical knowledge to verify that your technical skills will be of good for the company. A series of challenges will be directed towards you to solve quickly and record the whole process in a video or a series of videos. In the process of hiring of tech companies, programming skill will be your best friend to pass for the next round of interview.
The last and most important interview is the in-person interview. In the last round of the hiring procedure, most companies look forward to meeting the candidate in-person to evaluate further whether the candidate is suitable for the job title.
Not all companies take the candidates through only three interviews in their process of hiring. There can be multiple steps in a tech company's hiring procedure. But the internal process is more or less same even if there are additional steps to evaluate a candidate with sharply.