The spec you mention is USA only - I suggest European spec CO detectors @Geldard .
The alarm I linked to above ( Fire Angel CO-9D https://www.fireangel.co.uk/co-9d-manual/
The alarm will sound:
• Between 60 and 90 minutes when exposed to a minimum of 50ppm of CO.
• Between 10 and 40 minutes when exposed to a minimum of 100ppm of CO.
• Within 3 minutes when exposed to a minimum of 300ppm of CO.
The display shows anything over 10ppm.
35ppm The maximum allowable concentration for continuous exposure for healthy adults in any 8 hour period, as recommended by the
Occupational Safety and Health Administration (OSHA).
200ppm Slight headache, fatigue, dizziness, nausea after 2 - 3 hours.
400ppm Frontal headaches within 1 - 2 hours, life threatening after 3 hours.
800ppm Dizziness, nausea and convulsions within 45 minutes. Unconsciousness within 2
hours. Death within 2 - 3 hours.