Real-Time Crypto Alert System with Push Notifications

For real-time prices we use WebSocket from Binance (latency < 100ms), CryptoCompare (< 500ms), or Coinbase (< 200ms). For less urgent alerts, we use REST polling with a 30–60 second interval.

Backend subscribes to Binance WebSocket prices:

const WebSocket = require('ws'); const PAIRS = ['btcusdt', 'ethusdt', 'solusdt']; const ws = new WebSocket(`wss://stream.binance.com:9443/stream?streams=${PAIRS.map(p => p + '@ticker').join('/')}`); ws.on('message', (data) => { const { stream, data: ticker } = JSON.parse(data); const symbol = stream.replace('@ticker', '').toUpperCase(); const price = parseFloat(ticker.c); priceCache.set(symbol, price); alertEngine.checkAlerts(symbol, price); }); 

Alert engine: trigger checking and duplicate prevention

On each price update, we check all active alerts for that pair:

class AlertEngine { async checkAlerts(symbol: string, currentPrice: number): Promise<void> { const alerts = await alertRepository.getActiveAlerts(symbol); const triggered = alerts.filter(alert => { if (alert.type === 'ABOVE') return currentPrice >= alert.targetPrice; if (alert.type === 'BELOW') return currentPrice <= alert.targetPrice; if (alert.type === 'PERCENT_CHANGE') { const change = Math.abs((currentPrice - alert.basePrice) / alert.basePrice * 100); return change >= alert.percentThreshold; } return false; }); for (const alert of triggered) { await this.fireAlert(alert, currentPrice); } } private async fireAlert(alert: PriceAlert, price: number): Promise<void> { await alertRepository.deactivate(alert.id); await pushService.sendToUser(alert.userId, { title: `${alert.symbol} reached ${formatPrice(price)}`, body: this.buildAlertMessage(alert, price), data: { screen: 'price_detail', symbol: alert.symbol } }); await alertRepository.saveTriggeredAlert(alert, price); } } 

Deactivation before push dispatch is key. If the push fails, a retry will find the alert inactive—no duplicates. For critical cases we add a queue with retry and monitoring.

How do we guarantee push delivery without duplicates?

Deactivate the alert before calling the push service. Even if the send fails, a retry will find the alert inactive. For critical cases we include a queue with retry and monitoring. This ensures 100% delivery without duplicates.

UI on mobile platforms: creation, visualization, management

Creating an alert on iOS (SwiftUI)

The SwiftUI alert form allows users to set conditions. This iOS alert creation form is implemented with SwiftUI.

struct CreateAlertView: View { @State private var targetPrice: String = "" @State private var alertType: AlertType = .above let symbol: String let currentPrice: Double var body: some View { Form { Section("Condition") { Picker("Alert type", selection: $alertType) { Text("Price above").tag(AlertType.above) Text("Price below").tag(AlertType.below) Text("Percentage change").tag(AlertType.percentChange) } .pickerStyle(.segmented) HStack { Text("$") TextField("0.00", text: $targetPrice) .keyboardType(.decimalPad) } } Section { Text("Current price: \(formatPrice(currentPrice))").foregroundColor(.secondary) } Button("Create alert") { createAlert() } .disabled(targetPrice.isEmpty) } } } 

Visualizing Proximity to Price Threshold

We use a progress bar showing the current price relative to base and target. It helps the user gauge the distance to triggering. Example in Jetpack Compose alerts:

@Composable fun AlertProgressBar(currentPrice: Double, targetPrice: Double, basePrice: Double) { val progress = ((currentPrice - basePrice) / (targetPrice - basePrice)).coerceIn(0.0, 1.0) LinearProgressIndicator( progress = progress.toFloat(), modifier = Modifier.fillMaxWidth(), color = if (progress > 0.8) Color.Orange else MaterialTheme.colorScheme.primary ) Row(Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.SpaceBetween) { Text(formatPrice(basePrice), style = MaterialTheme.typography.labelSmall) Text("Target: ${formatPrice(targetPrice)}", style = MaterialTheme.typography.labelSmall) } } 

Repeating alerts with cooldown

By default, an alert fires once and is deactivated. The user can select a repeat option—then the alert reactivates N minutes after firing, to avoid spamming during volatile markets. The timeout is set individually, typically 5–30 minutes.

if (alert.isRepeating) { const cooldownMs = alert.cooldownMinutes * 60 * 1000; await alertRepository.scheduleReactivation(alert.id, Date.now() + cooldownMs); } 

Work process: from architecture to deployment

1. Requirements analysis — define alert types, price sources, push services.
2. Architecture design — server-client scheme, data flow, error handling.
3. Server-side engine development — Node.js 18, async/await, WebSocket stream with exponential backoff reconnection, MongoDB for alert storage.
4. Push service integration — APNs for iOS, FCM for Android.
5. Mobile UI creation — SwiftUI for iOS, Jetpack Compose for Android. The Android alert management interface uses Jetpack Compose.
6. Testing — price simulation, trigger verification, push sending.
7. Deployment and monitoring — server deployment, CI/CD integration.

Typical implementation mistakes

• No alert deactivation — leads to duplicates. Solution: deactivate before push.
• Using only REST without WebSocket — delays up to 60 seconds, users leave.
• Ignoring cooldown for repeating alerts — notification overload during volatility.

Timelines and what's included in the implementation

Implementation of a server-side alert engine with WebSocket price streaming, mobile UI for creating/managing alerts, push on trigger with history — 8–12 working days, starting from $12,000. Cost calculated individually per project requirements.

Full-cycle development includes:

• System architecture diagram (server + mobile clients)
• Server-side Node.js code with WebSocket streaming (Binance/CryptoCompare)
• Mobile modules in Swift (iOS) and Kotlin (Android) for creating/managing alerts
• Integration with push services (APNs and FCM)
• API and data schema documentation
• Testing and post-launch support

Comparing push services by latency and coverage:

For cross-platform solutions we use Firebase Cloud Messaging or a custom server with APNs+FCM.

We have 5+ years of experience in mobile application development and over 20 successful projects with push notifications. If you need a reliable Price Alerts implementation, contact us for a project evaluation. Our mobile push notifications are delivered instantly. Get a consultation: we'll tell you which solution fits your application.