diff --git a/lib/timex_datalink_client/protocol_7/eeprom/calendar/event.rb b/lib/timex_datalink_client/protocol_7/eeprom/calendar/event.rb
index 6cc1a33..33285c5 100644
--- a/lib/timex_datalink_client/protocol_7/eeprom/calendar/event.rb
+++ b/lib/timex_datalink_client/protocol_7/eeprom/calendar/event.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "active_model"
+
 require "timex_datalink_client/helpers/lsb_msb_formatter"
 
 class TimexDatalinkClient
@@ -7,16 +9,23 @@ class Protocol7
     class Eeprom
       class Calendar
         class Event
+          include ActiveModel::Validations
           include Helpers::LsbMsbFormatter
 
           FIVE_MINUTES_SECONDS = 300
 
-          attr_accessor :time, :phrase
+          validates :time, comparison: {
+            greater_than_or_equal_to: :device_time,
+            message: "%{value} must be greater or equal to device time!"
+          }
+
+          attr_accessor :time, :phrase, :device_time
 
           # Create an Event instance.
           #
           # @param time [::Time] Time of event.
           # @param phrase [Array<Integer>] Phrase for event.
+          # @raise [ActiveModel::ValidationError] One or more model values are invalid.
           # @return [Event] Event instance.
           def initialize(time:, phrase:)
             @time = time
@@ -24,6 +33,10 @@ def initialize(time:, phrase:)
           end
 
           def time_formatted(device_time)
+            @device_time = device_time
+
+            validate!
+
             device_time_midnight = Time.new(device_time.year, device_time.month, device_time.day)
             seconds = (time - device_time_midnight).to_i
             five_minutes = seconds / FIVE_MINUTES_SECONDS
diff --git a/spec/lib/timex_datalink_client/protocol_7/eeprom/calendar/event_spec.rb b/spec/lib/timex_datalink_client/protocol_7/eeprom/calendar/event_spec.rb
index d303214..aa5ff21 100644
--- a/spec/lib/timex_datalink_client/protocol_7/eeprom/calendar/event_spec.rb
+++ b/spec/lib/timex_datalink_client/protocol_7/eeprom/calendar/event_spec.rb
@@ -43,5 +43,16 @@
 
       it { should eq([0x7e, 0x0f]) }
     end
+
+    context "when time is 2021-12-10 15:28:15" do
+      let(:time) { Time.utc(2021, 12, 23, 18, 30, 20) }
+
+      it do
+        expect { phrase_value }.to raise_error(
+          ActiveModel::ValidationError,
+          "Validation failed: Time 2021-12-23 18:30:20 UTC must be greater or equal to device time!"
+        )
+      end
+    end
   end
 end