My SK698 works the first time, then stop working, how can I fix that?

Have you used the remote controls to turn off the alarm? 

If so, you've DISARMED the system. If you haven't ARMED it again, then it won't respond to new motion. This is why it seems like it only worked once.

The solution

First, ARM the system again using the remote control (press the lock button).

In the future, remember always to ARM the system after receiving and disabling an alert.

You may also choose not to disarm the system at all during an alert. The alert will only sound for 10 seconds, and then end. In this case, the system remains armed for the next alert.

About the SK698

The SK698 contains two motion sensors (SK615), two remotes (SK629), and an Alert. The whole system should work together right out of the box. If not, please check out the video on the product page here. 

After installing all the batteries, turn the sound switch and the power switch to ON. You've now ARMED the Alert. When motion is detected by the motion sensor, the Alert sounds. Now you can use the remote to turn the Alert sound OFF. That means you DISARM (press the unlock button) the Alert. If there is motion again at the sensor, the Alert will not sound because you just DISARMED the Alert.