Pairing
Press and hold reset button on the device for ± 5 seconds until the blue light blinks three times, release the reset button (the blue light will blink once more) and wait.
NOTE: When you fail to pair a device, try replacing the battery, this could solve the problem.
Or
Quickly press the front button on your Honeywell Smoke Detector three consecutive times in quick succession.
2 different advices, give it a try with the SmartThings hub in paring mode.
Grtn Ben