software - I used "keyword titan" when I had the money for it and I was happy with it. But there's also ahrefs, semrush, moz and countless others. I can't say which one of these is the best because I never used them (only used KT), but since they get so much praise on BHW I assume they're worth something
manual - just look at the domain names ranking on 1st page of google. If the top 5 domains are all known and/or big brands you're screwed. By big brands I don't mean facebook or amazon or wikipedia (although amazon could fall into the tech niche), I mean big brands in the tech niche, like sony, LG, or whatever.
Or, if there's no known / big brand in there check the websites' DA, RDs (Referring Domains), the number of keywords for which they're ranking, the amount of traffic they're getting, etc. and then do your due diligence. If the lowest DA you can find on the 1st page for your target keyword is 40, for example, you're up against tough competition. Likewise with the number of RDs or total number of backlinks: if the lowest RDs metric is in the 1000s you are again facing tough competition, especially if the number of keywords that the domain ranks for is in the millions and the traffic they're getting is in the 10s of 1000s.
On the other hand, if 2-3 websites ranking on google's 1st page have a DA of 30ish and their RDs and number of keywords that they rank for are low... I'd say your competition is weak. You still need to check their content, the RDs and PA of the specific URLs ranking for your target keyword and whatnot. But generally, domain authority > relevancy > content quality (in this order) is how google ranks websites nowadays