When your MSM-01 has not been used for a while it may need charging for a full 24 hour period, during this time the lights may not indicating charging for a while until the unit has enough charge.
If the sensor continues to not charge either the charger or port may be damaged. In this case please contact the support team who can assist with organising a repair or warranty claim.
The support team can be contacted at - support@avtreliability.com