Detect when DC motor is running?

[Tom18991]

Looking for advice on how to detect if a DC motor is running, using only its ground wire? No current flows when the motor is off.   I'd like to create a yes/no binary signal I can feed to a microcontroller -- high when the motor is running, low when it is not.  Is there a tried and true way to do this? 

[soldar]

No current is ever flowing on the ground wire. You mean "neutral"?

[themadhippy]

You mean "neutral"?

theres no neutral on DC

Looking for advice on how to detect if a DC motor is running, using only its ground wire?

low side current sensors  and a comparator?

[TimFox]

Do you need to check that the motor is not stalled?
The current is higher than normal under stall conditions with power applied.

[soldar]

You mean "neutral"?

theres no neutral on DC

I missed the DC part. My bad.

[Benta]

A glass tube reed switch with a coil wound around it. That'll even double as noise filter.

[rcjoy]

For industrial use, a DC current switch:

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/current_-a-_voltage_sensors_(ac_-a-_dc)/dc_current_switches#