The entry and exit zone alerts allow you to be automatically notified when the tracker enters or leaves a designated area. Very practical but are still complex because they are subject to the limitations of GPS technology. Here is a brief overview of the points to remember when setting up your first security zone.
The delay before the alert
The delay before issuing the alert will not be the same if it is an entry zone alert or an exit zone alert. We saw in a previous article that the GPS accuracy is affected by several criteria including being indoors or outdoors. This information is important: indoors the GPS accuracy will be inferior by nature (if the tracker picks up a GPS signal), leading to a risk of false exit zone exit alerts (the system might think that the tracer has come out of the zone while it is only a position error).
For this reason we have applied an extra margin of safety to the exit zone alert. This margin consists of a larger number of positions outside the zone before confirmation of the alert. This security is intended to minimise the number of false alerts so as not to unnecessarily generate a distressing situation.
If the tracker was indoors and did not pick up the GPS signal then it will take more time to retrieve it once outdoors, resulting in an additional offset before sending the exit zone alert (the time it takes to recover a GPS signal + safety margin of the exit zone).
This explains why the exit zone alerts are always slower to be received than entry alerts.
The shape of the zones
We are sometimes criticised for offering only one form of zone shape; this form does not always allow to faithfully adapt to the real zone. It is a choice on our part that echoes the points raised above, a commitment not to make false promises.
The idea is, above all, to be warned of an entry or an exit relative to a wide area, not compared to a garden fence for example. Because the limitations of GPS technology are such that the possibility of defining a “made to measure” zone would generate a great deal of frustration in the real world. It would be normal to expect to receive an alert once the portal has been crossed; which is impossible.
The exterior zones
When setting up a zone, you are asked to specify whether it is a “classic” zone or an outdoor zone. By outdoor zone we mean a perimeter that does not cover any interior place, such as a park for example.
If you check the outer zone option, we will remove the margin of safety of the exit zone, which will allow you to benefit from better reactivity during an alert (the tracer does not have the risk of positioning error from the inside, therefore there is no need to add this margin).
Always try to keep this information in mind when setting up a zone. This will help you choose the best configuration possible: entry and / or exit alert, zone radius, outside zone or not. Finally, avoid creating zones that are too close to each other, it could create conflicts between the margins of security of each of them (if the tracker is not officially released from the first zone before entering the second no alert can not be issued).