The best detector for the money that lasts 1 full year not 1 month (like those cheap ones from WalMart, Sporty's, etc. (check the instructions with these---they are only good 1 month after you open the package it comes in).
Call the QUANTUM GROUP INC. at 800-432-5599 and ask them for their CO(CARBON MONO) DETECTOR which at one time cost $9.95 + 2.00 postage.