Encender las alarmas

Pictures taken from Google Images, “Set the alarm bells ring”
Click on the image to watch a video of an alarm at a train station

Meaning:

If something sets the alarm bells ringing or if the alarm bells start to ring, you get the feeling that something bad is going on; you are in trouble.

Pictures taken from Google Images, “Set the alarm bells ringing”
Click on the image to watch a video on how the cell phones have set the alarms ringing for breast cancer

Origin:

Alarms are gadgets that people have devised in order to be forewarned of an impending problem or danger. Alarms have been used since people started living together to help each other or to defend their town from oncoming enemies. Horns and bells have usually been used as alarms. Alarms are activated by different events. It may be a fire, smoke or that a door has been opened by an authorized person.

Pictures taken from Google Images “Set the alarm bells ringing”
Click on the image to watch a video on how Fire Alarms set the alarm bells ringing for stress

Example: