For anyone who wants a simple notification if new cars are scanned.
You will need to create an input_text which holds last state with plates, I’ve named it: “current_cars_in_driveway”. You will also need to change the push service 
If you want to ignore some plates you can add it inside the [] in the variable ignored_plates
- id: '1613380190443'
alias: New cars in driveway
description: ''
trigger:
- platform: event
event_type: platerecognizer.vehicle_detected
condition: []
action:
- service: input_text.set_value
data:
value: '{{ updated_plates | join('','') }}'
entity_id: input_text.current_cars_in_driveway
- choose:
- conditions:
- condition: 'template'
value_template: '{{ new_plates|length > 0 }}'
sequence:
- service: notify.push
data:
message: '{{ ''A new car on driveway! Plate: '' + (new_plates | join('', '')) }}'
mode: single
variables:
ignored_plates: '{{ [] }}'
old_plates: '{{ states(''input_text.current_cars_in_driveway'').split('','') | list }}'
updated_plates: '{{ state_attr(trigger.event.data.entity_id, ''vehicles'') | map(attribute=''plate'') | list }}'
new_plates: '{{ updated_plates | reject(''in'', old_plates) | reject(''in'', ignored_plates) | list }}'