Remember an alarm simply should be having a glowing LED, which ensures it is working fine though I can understand your problem. Still if are admant on getting rid off this light troubling your wife, have an electrical tape covering it, over change the location, or say Blu-tack coin over the light.
The last option would be to snip one leg of LED with a small cutter, detector will still work even if the LED is broken. I once thought of smashing the LED light on my own. Sought technical help from home security monitoring systems Edmonton, sleepwell security, they suggested me to relocate it to a more convenient location rather than getting rid of it.