Don't worry about blood, urine, or breath tests. If you eat at or below 20g of net carbs a day for a couple days, you will be in ketosis. The measurement devices often tell you that ketones are present in your blood, urine, etc, but that doesn't really tell you if you are burning them. You can be testing low and still in ketosis since your body will be using the ketones rather than pissing them out.
If looking into this for real, don't waste your time, go to Ketogains.com and read their FAQ and check out their pinned posts on their FB. I started keto by other means/sets of info and ended up there over a period of 3-4 months, a couple years ago. They are the best at science based info in application of the diet. The main FB page has gotten a little out of control with a bunch of members that don't understand it, but the mods are extraordinary and the info available is fantastic.
Also, if you see some bullshit about high fat/low protien, just close that page and don't go back unless you are epileptic.
Calorie balance is still a thing. You can't just go crazy on bacon and drop weight. If you aren't keto yet, it will work for a short period of time, but then you body will catch up and you will start gaining weight.