Ato water alarm

[Wildreefs]

In need of some direction. A guy I help out in his tank asked me to find a way to put an Alarm in his 20 gallon ato reservoir, so it gives off a sound when it hits 5 inches or so . The ato alarm only goes off once it’s dry, he wants me to find an alarm that lets him know before it’s dry .

doesnt have an apex or any controller , looking for a stand alone solution to do this.

thank you

 

[Big G]

Amazon product

 

[Wildreefs]

Amazon product

Thanks.
Saltwater safe you think?

 

[dmsc2fs]

Thanks.
Saltwater safe you think?

ATO should be RODI and not SW?

 

[Wildreefs]

ATO should be RODI and not SW?

Yes correct , I should have said something more along the lines of fish safe, or drinking water safe, might just be meant for basement flood water etc that’s not being consumed