Selecting A Home Natural Gas Leak Detector: Advice, Please

Hello,
Trying to decide on a "good" Natural gas detector leak detector for house. Obviously, reliability is the most important issue.
NOT for the Propane tank kind; need for the normal piped in Natural Gas.
Can go crazy looking at the Amazon site and trying to decide. Most seem to be split very roughly 50% - 50% between those that say it is worthless and does not detect anything, and those that say it actually does work.
This seems to be more or less true for all the models and brand; Kidde, First Alert, and a few other imported ones from China with names I've never heard of.
A few questions, please:
a. Anyone know anything about the Techamor labeled ones ? New name for me. They seem to have gotten very good write-ups. It's a round cased one.
b. They all seem to be, surprisingly, plug in only, with a battery back up. Surprising. Anyone know why apparently plug-ins only ?
c. Expected to find units that were solely designed for Natural Gas. But most seem to be also for CO. Do they use two independent sensors ?
Should I be concerned if it is a compromise, and should only consider ones that only do one thing: detect Natural Gas ?
What do you folks use ? Convinced they work, etc. ?
Thanks, Bob
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On 5/10/2018 7:11 AM, Robert11 wrote:

Your nose can detect the mercaptan odorant at around 1 ppb. I would put a gas detector need below that of one for fire and another for CO.
Not sure how these detectors work but those for CO have a finite lifetime so maybe the gas ones do too.
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