# Function to report temp below zero, but suppress until temp rises above zero
**URL:** https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416
**Category:** General
**Created:** [19 December 2021 01:41 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416 "2021-12-19T01:41:53Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@cloudgenki](https://discourse.nodered.org/u/cloudgenki)
#### Post date: [19 December 2021 01:41 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/1 "2021-12-19T01:41:53Z")
Hi Guys,
I've written a function to email me when a temperature value is below zero.
The problem is that I want to **suppress further emails, until the temperature rise above zero**.
Can anyone point me in the right direction here?
Here's the function
if (msg.payload.Temperature \<= 32) {
msg.topic = "Alert: Aspen temp below zero !!"
return msg;
}
return null;
Thanks!!
---
### Author:  [@jbudd](https://discourse.nodered.org/u/jbudd)
#### Post date: [19 December 2021 01:49 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/2 "2021-12-19T01:49:54Z")
You can use a filter node, set to block unless msg.topic changes.
Your function would have to send a message rather than null when temperature \> 32.
That would result in an alert when the temperature dips and another when it rises again.
To prevent the rising notification use a switch node after the filter.
Edit - changed "filter" to "function" in line 2
---
### Author:  [@cloudgenki](https://discourse.nodered.org/u/cloudgenki)
#### Post date: [19 December 2021 01:50 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/3 "2021-12-19T01:50:39Z")
Hi Jbudd,
Thanks, I will try that now.
🙂
---
### Author:  [@drmibell](https://discourse.nodered.org/u/drmibell)
#### Post date: [19 December 2021 02:34 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/4 "2021-12-19T02:34:13Z")
This is such a basic part of system control that you probably should code it up yourself just for the experience. On the other hand, you will learn a lot by looking at the descriptions of contributed nodes that do the job. Try searching the library for "hysteresis."
---
### Author:  [@mickym2](https://discourse.nodered.org/u/mickym2)
#### Post date: [19 December 2021 22:35 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/5 "2021-12-19T22:35:02Z")
> [@cloudgenki](#):
>
> if (msg.payload.Temperature \<= 32) {
> msg.topic = "Alert: Aspen temp below zero !!"
> return msg;
> }
> return null;
I don't like to use function nodes at all. But here they may be useful - as you can use a context of the node - means you can store within the function node, if an alert has been already sent. In other words - with a context you can store a state which can be retrieved each time a message is received.
However you must define a clear if - else block. Here I modified the code of your function node to remember if you already have been alerted. Nevertheless you should probably use a hysteresis as recommended by @drmibell. Otherwise you get severeal messages when temperature changes around the threshold.
Here the code for using context within a function node:
```auto
var alerted = context.get('alerted') || false;
if (msg.payload.Temperature <= 32) {
msg.topic = "Alert: Aspen temp below zero !!"
context.set('alerted',true);
if (!(alerted)) return msg;
} else
{
context.set('alerted',false);
return null;
}
```
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [17 February 2022 22:35 UTC](https://discourse.nodered.org/t/function-to-report-temp-below-zero-but-suppress-until-temp-rises-above-zero/55416/6 "2022-02-17T22:35:19Z")
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