I use ketone test strips. I bought them on Amazon for £6 'ish, sorry I can't remember price exactly but I know they didn't cost loads. There's 125 in total in the box I bought. Some are nearly £10 or more but I only want something to give me an idea that I'm on the right track & that my body is now in ketosis. Where I want to be & stay 😉
All 3 of my kids HAD to try peeing on 1 each. My older son, who's doing keto with me, showed he was in ketosis. The other 2, who're on a regular nutrious diet, never changed the colour on the little stick. It was also my way of checking the sticks really work.
I'll give you the link to the ones I bought but there's loads of other brands & places to buy them but it should give you a better idea of what I'm using:
https://www.amazon.co.uk/gp/aw/d/B084VKSW5G?psc=1&ref=ppx_pop_mob_b_asin_title
Good Luck on your journey xxx