It is possible the battery is complete out and they need to be recharged. The sunlight in the winter is very week but that should improve in spring. Do you have an incandescent lamp, if so you can use it to charge the sensors for 3 days and they should be back to live.
Could you please send us email to email@example.com with your Netro account registered email?
We will have our technician look into this issue.
I sent an email on the 4th to firstname.lastname@example.org and have not even received an acknowledgment.
We have received your email and will send you a replacement unit.