I have a CO alarm and it is a Nighhawk and it is about 10 years old and it was left over from when we moved in here in 1999. It is one of those digital read out displays. Anyway, should I get a new one b/c I have no manuel for it and don't know how it works and plus I played arround with the buttons when I was a little kid and might of messed it up a bit. You know you need to replace your smoke alarms every 10 years. Same with CO alarms? Any advise?

Hi Doug
You are correct about the life time of a CO2 alarm it is 10 years. No Idea about prices of a new one Sry.
More info www.brkelectronics.com/faqs/co_alarms.htm

CO detectors are not very expensive. You can buy a plug in style detector at any hardware store for around $25 - $40. It is important to get a new one occasionally because the method of detection is a rather sensitive part and uses elements that do not have a half-life longer than 10 years.

Ace Hardware Site

I recommend using a brand name. First Alert is widely recognized as a dependable brand. The problem with CO detectors is that they are so sensitive that you will get false alarms. It's especially troublesome to get false alarms with this type of thing because you can become unsure when you actually have a serious problem and end up unplugging the thing and going to bed. I know someone who had a CO detector that constantly gave false alarms and then went off one night. They debated just going back to bed but called the Fire Department instead and found a leak... saved their lives.