diff --git a/src/Monitor.ts b/src/Monitor.ts
index 5b8c448..c276a08 100644
--- a/src/Monitor.ts
+++ b/src/Monitor.ts
@@ -261,16 +261,22 @@ export class Monitor extends TypedEmitter<IMonitorEvents> {
         this.checkChangedValue(previousState, state, 'battery.runtime', (value) => this.emit('BATTERY_RUNTIME', Number(value), value));
 
         let variableChanged = false;
-        Object.keys({
-            ...previousState,
-            ...state
-        }).forEach((k) => {
+        const processKey = (k: string) => {
             const key = k as nutVariablesNames;
             this.checkChangedValue(previousState, state, key, () => {
                 this.emit('VARIABLE_CHANGED', key, previousState[key] ?? '', state[key] ?? '', previousState, state);
                 variableChanged = true;
             });
-        });
+        };
+
+        for (const key of Object.keys(state)) {
+            processKey(key);
+        }
+        for (const key of Object.keys(previousState)) {
+            if (!(key in state)) {
+                processKey(key);
+            }
+        }
 
         // one variable changed ?
         if (variableChanged) {
diff --git a/tests/Monitor.tests.ts b/tests/Monitor.tests.ts
new file mode 100644
index 0000000..22d501c
--- /dev/null
+++ b/tests/Monitor.tests.ts
@@ -0,0 +1,175 @@
+import { beforeEach, describe, expect, it, jest } from '@jest/globals';
+import { Monitor } from '../src/Monitor.js';
+import { NUTClient } from '../src/NUTClient.js';
+import { UPS } from '../src/UPS.js';
+import { ENUTStatus } from '../src/ENUTStatus.js';
+
+describe('Monitor', () => {
+    let mockClient: jest.Mocked<NUTClient>;
+    let mockUps: jest.Mocked<UPS>;
+    let monitor: Monitor;
+
+    beforeEach(() => {
+        mockClient = {
+            getUPS: jest.fn()
+        } as unknown as jest.Mocked<NUTClient>;
+
+        mockUps = {
+            listVariables: jest.fn()
+        } as unknown as jest.Mocked<UPS>;
+
+        monitor = new Monitor(mockClient, 'testUps');
+        // @ts-ignore
+        monitor.ups = mockUps;
+    });
+
+    it('should not emit events on the first loop', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+        mockUps.listVariables.mockResolvedValueOnce({
+            'battery.charge': '100',
+            'battery.status': ENUTStatus.OL
+        });
+
+        // @ts-ignore
+        await monitor._loopFn();
+
+        expect(spy).not.toHaveBeenCalledWith('VARIABLE_CHANGED', expect.anything(), expect.anything(), expect.anything(), expect.anything(), expect.anything());
+    });
+
+    it('should emit VARIABLE_CHANGED when a variable is modified', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+
+        // Initial state
+        // @ts-ignore
+        monitor.previousState = {
+            'battery.charge': '100'
+        };
+        // @ts-ignore
+        monitor.communication = true;
+
+        // New state
+        mockUps.listVariables.mockResolvedValueOnce({
+            'battery.charge': '90'
+        });
+
+        // @ts-ignore
+        await monitor._loopFn();
+
+        expect(spy).toHaveBeenCalledWith(
+            'VARIABLE_CHANGED',
+            'battery.charge',
+            '100',
+            '90',
+            { 'battery.charge': '100' },
+            { 'battery.charge': '90' }
+        );
+        expect(spy).toHaveBeenCalledWith('VARIABLES_CHANGED', { 'battery.charge': '100' }, { 'battery.charge': '90' });
+    });
+
+    it('should emit VARIABLE_CHANGED when a variable is added', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+
+        // Initial state
+        // @ts-ignore
+        monitor.previousState = {
+            'battery.charge': '100'
+        };
+        // @ts-ignore
+        monitor.communication = true;
+
+        // New state
+        mockUps.listVariables.mockResolvedValueOnce({
+            'battery.charge': '100',
+            'ups.load': '10'
+        });
+
+        // @ts-ignore
+        await monitor._loopFn();
+
+        expect(spy).toHaveBeenCalledWith(
+            'VARIABLE_CHANGED',
+            'ups.load',
+            '',
+            '10',
+            { 'battery.charge': '100' },
+            { 'battery.charge': '100', 'ups.load': '10' }
+        );
+    });
+
+    it('should emit VARIABLE_CHANGED when a variable is removed', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+
+        // Initial state
+        // @ts-ignore
+        monitor.previousState = {
+            'battery.charge': '100',
+            'ups.load': '10'
+        };
+        // @ts-ignore
+        monitor.communication = true;
+
+        // New state
+        mockUps.listVariables.mockResolvedValueOnce({
+            'battery.charge': '100'
+        });
+
+        // @ts-ignore
+        await monitor._loopFn();
+
+        expect(spy).toHaveBeenCalledWith(
+            'VARIABLE_CHANGED',
+            'ups.load',
+            '10',
+            '',
+            { 'battery.charge': '100', 'ups.load': '10' },
+            { 'battery.charge': '100' }
+        );
+    });
+
+    it('should handle status changes and emit corresponding events', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+
+        // Initial state
+        // @ts-ignore
+        monitor.previousState = {
+            'battery.status': ENUTStatus.OL
+        };
+        // @ts-ignore
+        monitor.communication = true;
+
+        // New state
+        mockUps.listVariables.mockResolvedValueOnce({
+            'battery.status': ENUTStatus.OB
+        });
+
+        // @ts-ignore
+        await monitor._loopFn();
+
+        expect(spy).toHaveBeenCalledWith('ONBATT');
+    });
+
+    it('should handle communication loss and recovery', async () => {
+        const spy = jest.spyOn(monitor, 'emit');
+
+        // Initially communicating
+        // @ts-ignore
+        monitor.communication = true;
+
+        // Communication fails
+        mockUps.listVariables.mockRejectedValueOnce(new Error('fail'));
+
+        // @ts-ignore
+        await monitor._loopFn();
+        expect(spy).toHaveBeenCalledWith('NOCOMM');
+        // @ts-ignore
+        expect(monitor.communication).toBe(false);
+
+        // Communication recovers
+        mockUps.listVariables.mockResolvedValueOnce({ 'battery.charge': '100' });
+        // @ts-ignore
+        await monitor._loopFn();
+        expect(spy).toHaveBeenCalledWith('COMMOK');
+        // @ts-ignore
+        expect(monitor.communication).toBe(true);
+    });
+});