diff --git a/install.sh b/install.sh
index a11696c..a457e20 100644
--- a/install.sh
+++ b/install.sh
@@ -9,19 +9,74 @@ fi
 PROJECT_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 APP_ROOT="/opt/serial-bridge"
 CONFIG_ROOT="/etc/serial-bridge"
+VENV_PY="${APP_ROOT}/.venv/bin/python"
+REQ_HASH_FILE="${APP_ROOT}/.requirements.sha256"
+NEEDS_APT=0
+NEEDS_VENV=0
+NEEDS_PIP=0
 
-apt-get update
-apt-get install -y \
-  python3 \
-  python3-venv \
-  python3-pip \
-  hostapd \
-  dnsmasq \
-  iw \
-  wpasupplicant \
-  iproute2 \
-  rfkill \
+REQUIRED_PACKAGES=(
+  python3
+  python3-venv
+  python3-pip
+  hostapd
+  dnsmasq
+  iw
+  wpasupplicant
+  iproute2
+  rfkill
   i2c-tools
+)
+
+is_installed() {
+  [[ -d "${APP_ROOT}/src" ]] && [[ -f "/etc/systemd/system/serial-bridge.service" ]]
+}
+
+all_packages_installed() {
+  local pkg
+  for pkg in "${REQUIRED_PACKAGES[@]}"; do
+    if ! dpkg -s "${pkg}" >/dev/null 2>&1; then
+      return 1
+    fi
+  done
+  return 0
+}
+
+compute_req_hash() {
+  sha256sum "${PROJECT_ROOT}/requirements.txt" | awk '{print $1}'
+}
+
+mode="install"
+if is_installed; then
+  mode="update"
+fi
+
+echo "Modus: ${mode}"
+
+if ! all_packages_installed; then
+  NEEDS_APT=1
+fi
+
+if [[ ! -x "${VENV_PY}" ]]; then
+  NEEDS_VENV=1
+fi
+
+current_req_hash="$(compute_req_hash)"
+stored_req_hash=""
+if [[ -f "${REQ_HASH_FILE}" ]]; then
+  stored_req_hash="$(cat "${REQ_HASH_FILE}" 2>/dev/null || true)"
+fi
+if [[ "${NEEDS_VENV}" -eq 1 ]] || [[ "${current_req_hash}" != "${stored_req_hash}" ]]; then
+  NEEDS_PIP=1
+fi
+
+if [[ "${NEEDS_APT}" -eq 1 ]]; then
+  echo "Installiere fehlende Systempakete..."
+  apt-get update
+  apt-get install -y "${REQUIRED_PACKAGES[@]}"
+else
+  echo "Systempakete bereits vorhanden, ueberspringe apt."
+fi
 
 install -d -m 755 "${APP_ROOT}" "${APP_ROOT}/src" "${APP_ROOT}/templates" "${APP_ROOT}/static" "${CONFIG_ROOT}"
 
@@ -30,9 +85,19 @@ cp -a "${PROJECT_ROOT}/templates/." "${APP_ROOT}/templates/"
 cp -a "${PROJECT_ROOT}/static/." "${APP_ROOT}/static/"
 cp "${PROJECT_ROOT}/requirements.txt" "${APP_ROOT}/requirements.txt"
 
-python3 -m venv "${APP_ROOT}/.venv"
-"${APP_ROOT}/.venv/bin/pip" install --upgrade pip
-"${APP_ROOT}/.venv/bin/pip" install -r "${APP_ROOT}/requirements.txt"
+if [[ "${NEEDS_VENV}" -eq 1 ]]; then
+  echo "Erstelle Python venv..."
+  python3 -m venv "${APP_ROOT}/.venv"
+fi
+
+if [[ "${NEEDS_PIP}" -eq 1 ]]; then
+  echo "Aktualisiere Python-Abhaengigkeiten..."
+  "${APP_ROOT}/.venv/bin/pip" install --upgrade pip
+  "${APP_ROOT}/.venv/bin/pip" install -r "${APP_ROOT}/requirements.txt"
+  echo "${current_req_hash}" > "${REQ_HASH_FILE}"
+else
+  echo "requirements.txt unveraendert, ueberspringe pip install."
+fi
 
 install -m 644 "${PROJECT_ROOT}/config/hostapd.conf" "${CONFIG_ROOT}/hostapd.conf"
 install -m 644 "${PROJECT_ROOT}/config/dnsmasq.conf" "${CONFIG_ROOT}/dnsmasq.conf"
@@ -56,4 +121,4 @@ systemctl daemon-reload
 systemctl enable serial-bridge.service
 systemctl restart serial-bridge.service
 
-echo "Installation abgeschlossen. Logs: journalctl -u serial-bridge -f"
+echo "Fertig (${mode}). Logs: journalctl -u serial-bridge -f"