How calving sensors work — and the no-SIM alternative
Updated 1 July 2026
Calving sensors and calving-alert systems aim to give you earlier warning that a cow may be calving, so you can be there when it matters. Here is how the main approaches work, and where a no-SIM system fits in.
What a calving-alert system does
Most calving-alert systems watch for a change that tends to happen around calving and then send the farmer a notification. The common approaches are tail-movement sensors, activity and behaviour monitors, and cameras. They do not replace checking the cow — they aim to prompt a check at the right time.
- Tail-movement sensors detect the tail-raising associated with contractions
- Activity monitors watch for changes in movement and restlessness
- Cameras let you watch remotely, but still rely on you watching
Why mobile signal matters
Many calving sensors send alerts by SMS or mobile app, which means they need a mobile signal at the animal — in the shed, yard or field. On a lot of British farms that signal is patchy or missing exactly where calving happens. If the alert cannot get out, the system cannot help.
The no-SIM, farm-owned alternative
Instead of putting a SIM and a mobile contract in every device, a farm-owned network uses a low-power, long-range link back to a gateway on the farm. HerdHalo Calve works this way: there is no SIM card in the tag, and it is designed to keep reporting across sheds, yards and fields where mobile coverage is poor.
What a calving alert can and cannot do
A calving alert is an aid, not a diagnosis. HerdHalo Calve monitors activity and movement patterns and alerts you to attention-worthy changes during calving windows — it does not diagnose pregnancy and does not replace stockmanship, veterinary advice or direct animal checks.