pop up timer on chicken didn't pop up
Not only are they sometimes defective, they are nearly always inaccurate. Get yourself a good instant read thermometer. If those are too expensive, get a analog thermometer that reads a little slower but is still more accurate than the "buttons" the meat processing plants stick into their poultry (and some other meats)
The USDA says that, to be safe for human consumption, chicken should be at a minimum internal temperature of 165 °F, as measured using a food thermometer. But it's certainly OK to cook chicken to a higher temperature if there's any doubt about its being done.
To check the internal temperature, stick the probe of your thermometer into the area nearest the innermost part of the thigh and wing and the thickest part of the breast. Be careful not to allow the thermometer to make any firm contact with bones.
I don't trust those things any further than I can throw a large Turkey. I use a Thermapen for fast accurate readings. http://www.thermoworks.com/products/thermapen/splashproof_thermapen.html Yes they are expensive. Its a Type K Thermocouple. IMHO the speed and accuracy are worth every penny.
Whatever you use, you should check the accuracy against boiling water. To do this, you must know what temperature water boils at your altitude. http://www.csgnetwork.com/h2oboilcalc...