Carbon monoxide detector keeps beeping?

I have two carbon monoxide detector. My upstair carbon monoxide detector keeps beeping every 2-4 minutes. It also has a number saying 52. The carbon monoxide downstair appears to be fine, althrough it doesnt have that displaying number thing. I tried switching the carbon monoxide with each other, and now neither beeps anymore. But one of the carbon monoxide detetor(the one from upstair then switch to downstair) still says 52. Should i be concern?