Suggestion for a device that senses voltage? Septic Tank Alert

I have a septic tank and a manual alert system (buzzer) essentially a wire connected to a float down in the tank closes the circuit and sets off the alarm. I'd like to keep the manual audible alarm but also add a device that can send a notification when this goes off. Anyone ever done this? A device that can sense voltage being turned on?

My other thought was a sound device strapped right to it (it's loud) but that seems hoaky. So does a bunch of wires and relays. Was hoping someone knew of something...obviously needs to work in HE.

From the manual:

Switching mechanism operates on low voltage and is
isolated from power line to reduce possibility of shock

Can be use with any UL Listed / Recognized switching
mechanism rated to include 1 amp, 12 VAC load

across the buzzer, add the coil of a 12vac relay. Now you have contacts that can go into many Door Sensors. They often have an internal pair of screws to use for just such a purpose.

This escalated quickly tonight... sooooo I went down to measure the actual voltage...while I'm there I find out that the manual alarm was plugged into a UPS...and that had died (ironic right) and the whole alarm was dead. Plugged it in and got an alarm. Yep you guessed it! Wires had shorted in the tank and tripped the breaker for the pump. So the whole reason for an alarm....poof. Just spent the last hour fixing that.

Per your original message, you have 12vac... This connects to a buzzer with a switch on one leg. When the switch closes, there's 12vac across the buzzer. If you purchase a 12ac relay, connect the coil across the 2 buzzer wires. Now, when the switch closes, there's 12vac across BOTH the buzzer and the relay's coil, energizing both. The buzzer buzzes, the relay goes click.

The contacts of the relay are what are called "dry contact" meaning no voltage. (Remember when electricity was called "juice"? Yea, 'wet' means has Juice, 'dry' means no Juice.) The Ecolink door sensor In my pics have an internal port for dry contacts. Meaning the Ecolink has voltage and when the relay's contacts close, it will see that and send a ZWave message.

Was just pulling the parts together to test this out.

Decided to make my own as I didn't have a 12vAC relay. Took a 12v (AC/DC)transformer run through the float to a 12v DC relay. Used the contacts to drive a Monoprice Garage door sensor (has dry contact input). Last step will be to find a proper 12v DC buzzer.

Just be aware we are talking about 12VAC and not 12VDC here.

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yep, hence me not having any 12v ac relays and only some 12v DC relays (automotive) laying around. That's why I used an AC/DC transformer. (and why I couldn't use the buzzer). I see above I wasn't clear on that. I'll fix it.

You don't have to fix anything above. I am just pointing it out incase your meter is on DC measurements and get no voltage that's all.

Fixed properly with 12vAC relay DPDT. One set of contacts drives the monoprice sensor, the other set drives the original buzzer/light.

Necro Thread Revival,

@csteele, I'm trying to connect the contact inputs of the DWZWAVE2.5-ECO to a float contact on my Septic Tank float system. When I connect the leads from the Sensor to the float contact connection points in my septic panel, the sensor reads closed. My presumption is that means the float contact is "normally closed", so I set the sensor to go off when it changed state to "open". Unfortunately, in the last 24 hours it hasn't reported an "open".

Question, are the two pins on the DWZWAVE2.5-ECO for the contact, polarized (or rather is the connection to the float polarized I guess). And if so, would it matter? In other words if it's polarized, does the sensor just read backwards, or does it become always "closed"?

I'm far from an electronics expert, this is a bit beyond my experience! Any tips you might have would be crazy useful.


Screen Shot 2020-05-26 at 2.29.11 PM

Normally a float contact is a switch. Mine is a magnet inside a 'ring' (the float) and a reed switch in the sealed center barrel. There's no polarity for a reed switch. The screws inside the door sensor ideal for any kind of 'dry contact' switch, such as the reed.

The particular float switch I am using has two wires and the float can be inverted.. The float floats.. at some fixed 'height'. Let's pretend there's a 1/4" of the float above the surface of the liquid. The magnet will either be up near the top, above the liquid or flipped over, will be well below the liquid surface. The reed inside is fixed. So by flipping the float over, you alter the way the switch works.. Normally Open or Normally Closed. (NO / NC)

So.. your question is more about what float switch you own. :smiley: Solid state? yea, maybe polarized.

I found the Ecolink Door Sensor to be quite functional. I have a pressure sensor that is basically a variable resistor. No pressure and the thing is 1 meg ohm of resistance or more. When I push my thumb on it, it drops to a range of a few hundred ohms. That's a very nice range. :slight_smile: The Ecolink door sensor fires when the pressure is about a CR123 battery sitting on the sensor.

In other words, the contacts inside the Door Sensor is forgiving of contact & wire resistance.

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Unfortunately, I have no idea what sort of float switch is in the system. There are three of them, and it appears from the drawing that I have, that they are normally open, but it's not 100% clear to me.

I'll have to look at the drawing some more, and take it to my EE friend at work and see if he can puzzle it out. It may be I have to do something like what you suggested to @jrfarrar and measure (somehow) when the alarm goes off (it has a buzzer and a light, but they both appear to be 120VAC).

Thank You!


Post the diagram.

If you want to trigger from the 120V buzzer/light circuit, that is real easy. Use a 120V relay, and just hook the contact sensor to the N.O. terminals.

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Here's the drawings for my system.

Thanks for looking!


Easy. You need a 120V AC relay. The coil of the relay will go to terminals A1 and A2 of the panel. When there is an alarm, A1 and A2 are active powering the relay.

The other terminals of the relay, the normally open terminals (N.O.) will go to a contact sensor just like in the picture @csteele shows above.

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Wow! That's awesome thank you! Let me see if 8 can find a suitable part, and I can link it here for confirmation. Thanks again to both yourself and @csteele!


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Probably a bit overkill, but I think this would work, and be easy to use as it already has pigtails. It also has a pilot light that would illuminate when the relay was on as added indication of alarm.

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Thanks! My first thought was it looked too large, but I think I could mount it to one of the knockouts on the bottom of the control box if necessary. Thank You. @ only $12 and change, I can't go wrong anyway! :grinning:

Done, ordered. Here on Thursday!