I have had this happen a couple of times over the years. As suggested, hold the test button on the DS10A until it resets, and creates a new code. But with the DS7000, you will have to clear the console (remove 9v battery and unplug) and re-enter all the sensors and remotes again. In my case, it wasn't low batteries, the console just decided to drop that sensor.
NO NO NO!
holding the test button down as I said in my other post does NOT - repeat - does NOT - reset the ds10 security code!!!!!!!!!!!!
follow up with one more short push of test button to make it work again...... this sequence simply forces the ds10 to re-evaluate its incorrect batt value and fix itself.....
to force a new security code, remove batts for a long time (read istrucs or ask as I dont know how long is required) and then put back in. NOW u have a new code and must reteach DS7000. I left batt compartment open on a few ds10.s lately..,, last night it would not set alarm on.... checked and found a cat had pulled one batt out! THAT caused a new security code and reporgram required since it was who knows how long out.
add a perhaps if.....: if u found a new securioty code was generated by holding down test button and waiting ofr multiple blinks of LED and did not then follow up with another short push on test button, then perhaps that does reset the security code; MY scheme is the two step long push then short push and I gaurantee it does not reset security code. we all know how painful that is on ds7000. I needed to temper my reply to say if no second f-up push of test button is unkown state to me so may be crash and burn and new security code. but my two step push DOES keep security code - i tested it like 24 times to be sure before posting...............