Need recommendation for home CO detector, want ppm readout.

I've had excellent results and no false alarms with the battery operated Kiddie w/display.
I've had them (four units) for two+ yrs now...

https://www.amazon.com/dp/B004Y6V5CI/ref=sxr_rr_xsim_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=4518303533042278392&pd_rd_wg=jeOvW&pf_rd_r=E553XNR13QTME21TJH8X&pf_rd_s=desktop-rhs-carousels&pf_rd_t=301&pd_rd_i=B004Y6V5CI&pd_rd_w=QiYx8&pf_rd_i=co+detector&pd_rd_r=682060ea-d239-454e-9635-e6048f79614f&ie=UTF8&qid=1527093610&sr=1

The CO detector I mentioned above has always been very close to the readings I've seen on my professional grade CO detector (see below). It won't display or alert below 40ppm (IIRC) due to federal regulations, but it will display the actual low level ambient/peak CO amounts if you press the Peak button. My old boiler had a small CO leak... the Kiddie would indicate (by pressing the Peak button) maybe 12-16PPM in the basement if the boiler had been running for an hour or two. Sometimes I would double check it with the Sensorcon.. they were always within a few PPM of each other. It was pretty impressive for a $25 device.

For real time readings all the way down to 1ppm I use the Sensorcon Inspector.

https://sensorcon-sensing-products-by-molex.myshopify.com/products/portable-carbon-monoxide-detector-meter?utm_medium=cpc&utm_source=googlepla&gclid=EAIaIQobChMIwbzn7Kuc2wIVzSWBCh0Q1AwJEAYYASABEgIdnPD_BwE&variant=4193480964

Quite a few of the professionals here use the same CO meter on the job because they could potentially be walking in to a toxic boiler room, etc.
I leave mine on all the time in a prominent location just outside the kitchen. I've changed the battery once in 2+ yrs of use.

https://www.trutechtools.com/installedco has the Defender LL6070 Low Level Carbon Monoxide Monitor and CO Experts models. I've had a number of the Defender models installed for 6 months with good results. Catches the low levels when oven is dirty. Also hit a button and it tells you the last CO reading, PPM level and how long it lasted. I used to use NSI but they made it available only via having to pay plumbers to install it.