diff --git a/deploy/apps/apps.json b/deploy/apps/apps.json
index 52ba456..5fa5aaa 100644
--- a/deploy/apps/apps.json
+++ b/deploy/apps/apps.json
@@ -96,6 +96,14 @@
       "ver": "1.0",
       "desc": "Send a mesh DM ping to any contact and measure round-trip time. Includes your GPS position so both sides see distance and bearing. Auto-replies to incoming pings. Contributed by samuelcoustet.",
       "requires": "sdk_ext"
+    },
+    {
+      "id": "mecp",
+      "name": "MECP",
+      "ver": "1.0",
+      "desc": "Emergency messages in MECP code: pick severity and codes, add people and position, post to a channel. Decodes MECP lines into words. Code table: MECP by xiang-dev-1, CC BY 4.0.",
+      "requires": "sdk_ext",
+      "seed": false
     }
   ]
 }
diff --git a/deploy/apps/mecp/1.0/mecp.json b/deploy/apps/mecp/1.0/mecp.json
new file mode 100644
index 0000000..9936023
--- /dev/null
+++ b/deploy/apps/mecp/1.0/mecp.json
@@ -0,0 +1 @@
+{"id":"mecp","name":"MECP","ver":"1.0","desc":"Write and read MECP emergency messages: pick a severity and codes, add the head count and your position, post to a channel. Decodes MECP lines into words. Code table: MECP by xiang-dev-1, CC BY 4.0.","requires":"sdk_ext"}
diff --git a/deploy/apps/mecp/1.0/mecp.lua b/deploy/apps/mecp/1.0/mecp.lua
new file mode 100644
index 0000000..f811871
--- /dev/null
+++ b/deploy/apps/mecp/1.0/mecp.lua
@@ -0,0 +1,470 @@
+-- MECP: write and read Mesh Emergency Communication Protocol messages.
+-- A MECP message is plain text, MECP/<severity>/<codes> [extras], so it travels
+-- over any channel and every reader with a code table sees it in their own
+-- language. Pick a severity and the codes; the app adds the head count and your
+-- position, shows the exact text, and posts it to the channel you choose.
+-- Decode turns a MECP line back into words, and lines heard on your channels
+-- while the app is open are listed decoded. Requires: sdk_ext (channel send).
+
+local ui, sys, mesh, store = wada.ui, wada.sys, wada.mesh, wada.store
+local C = ui.colors
+local clear = ui.clear or function() end
+
+-- English code table from MECP (github.com/xiang-dev-1/MECP, languages/en.json),
+-- by xiang-dev-1, CC BY 4.0. The protocol itself is CC0.
+local CATS = {
+  { id = "M", name = "Medical" },
+  { id = "T", name = "Terrain / Infrastructure" },
+  { id = "W", name = "Weather / Environment" },
+  { id = "S", name = "Supplies" },
+  { id = "P", name = "Position / Movement" },
+  { id = "C", name = "Coordination" },
+  { id = "R", name = "Response" },
+  { id = "D", name = "Drill / Test" },
+  { id = "L", name = "Life / Leisure" },
+  { id = "X", name = "Threat / Security" },
+  { id = "H", name = "Have / Offer Resources" },
+  { id = "B", name = "Beacon" },
+}
+local CODES = {
+  M01 = "Injury",
+  M02 = "Unconscious person",
+  M03 = "Breathing difficulty",
+  M04 = "Cardiac event",
+  M05 = "Hypothermia",
+  M06 = "Severe bleeding",
+  M07 = "Fracture / immobile",
+  M08 = "Burns",
+  M09 = "Multiple casualties",
+  M10 = "Deceased",
+  M11 = "Animal bite / sting",
+  M12 = "Allergic reaction / anaphylaxis",
+  M13 = "Poisoning / toxic exposure",
+  M14 = "Persons located alive",
+  M15 = "Area searched, no victims found",
+  T01 = "Road blocked",
+  T02 = "Bridge out",
+  T03 = "Building collapsed",
+  T04 = "Flooding",
+  T05 = "Landslide",
+  T06 = "Power out",
+  T07 = "Fire",
+  T08 = "Avalanche",
+  T09 = "Path impassable",
+  T10 = "Shelter available",
+  T11 = "Drowning / water rescue needed",
+  T12 = "Water contamination",
+  T13 = "Earthquake",
+  T14 = "Gas leak",
+  T15 = "Chemical spill / HAZMAT",
+  T16 = "Vehicle accident",
+  T17 = "Vehicle fire",
+  W01 = "Storm approaching",
+  W02 = "Visibility zero",
+  W03 = "Extreme cold",
+  W04 = "Extreme heat",
+  W05 = "Air quality danger",
+  W06 = "Tsunami / tidal surge warning",
+  S01 = "Need water",
+  S02 = "Need food",
+  S03 = "Need medication",
+  S04 = "Need battery / power",
+  S05 = "Need fuel",
+  S06 = "Need tools / equipment",
+  P01 = "Stranded / stuck",
+  P02 = "Evacuating toward",
+  P03 = "Sheltering in place",
+  P04 = "En route to",
+  P05 = "At GPS coordinates",
+  P06 = "Lost",
+  P07 = "Group separated",
+  C01 = "Send rescue",
+  C02 = "Need transport",
+  C03 = "Relay this message",
+  C04 = "Confirm received",
+  C05 = "How many people",
+  C06 = "What is status",
+  C07 = "Can you reach",
+  C08 = "Rendezvous at",
+  R01 = "Acknowledged",
+  R02 = "Help coming",
+  R03 = "ETA [minutes]",
+  R04 = "Cannot assist",
+  R05 = "Redirecting to",
+  R06 = "Stand by",
+  R07 = "Situation resolved / all clear",
+  D01 = "This is a drill",
+  D02 = "This is a test",
+  D03 = "End of drill",
+  D04 = "Ignore previous, sent in error",
+  L01 = "Beer / drinks",
+  L02 = "Coffee",
+  L03 = "Food ready",
+  L04 = "Summit reached",
+  L05 = "At camp",
+  L06 = "Running late",
+  L07 = "Good signal here",
+  L08 = "Photo opportunity",
+  L09 = "Wildlife spotted",
+  L10 = "Beautiful view",
+  L11 = "Trail conditions good",
+  L12 = "Trail conditions bad",
+  L13 = "Need a break",
+  L14 = "Heading home",
+  L15 = "Good morning / check-in",
+  L16 = "Good night",
+  L17 = "Thank you",
+  L18 = "Having fun",
+  L19 = "Festival / event here",
+  L20 = "Node test / ping",
+  X01 = "Dangerous person / threat nearby",
+  X02 = "Area unsafe, avoid",
+  X03 = "Gunfire / explosions heard",
+  X04 = "Civil unrest / crowd danger",
+  X05 = "Theft / looting reported",
+  X06 = "Authorities / emergency services present",
+  X07 = "Checkpoint / road closure (authority)",
+  H01 = "Have water available",
+  H02 = "Have food available",
+  H03 = "Have medical supplies",
+  H04 = "Have power / charging",
+  H05 = "Have fuel",
+  H06 = "Have tools / equipment",
+  H07 = "Have shelter / space for [N]pax",
+  H08 = "Have transport / vehicle",
+  B01 = "Automated distress beacon active, sender may be unresponsive",
+  B02 = "Beacon acknowledged, reduce transmission rate",
+  B03 = "Cancel beacon, I am OK",
+}
+
+local SEV     = { [0] = "MAYDAY", "URGENT", "SAFETY", "ROUTINE" }
+local SEV_SUB = { [0] = "life-threatening", "time-critical", "important", "normal" }
+local MAX_LEN    = 180   -- wada.mesh.send refuses longer text
+local KEEP_HEARD = 20
+local PAD = 6
+
+-- Codes per category, in code order, for the pickers.
+local CAT_CODES = {}
+for code in pairs(CODES) do
+  local c = code:sub(1, 1)
+  CAT_CODES[c] = CAT_CODES[c] or {}
+  table.insert(CAT_CODES[c], code)
+end
+for _, list in pairs(CAT_CODES) do table.sort(list) end
+
+local app = {}
+local W, H = 240, 240
+local st = { sev = 3, codes = {}, pax = 0, gps = true, note = "", chan = nil }
+local heard = {}         -- {from, raw, words, sev}, newest first, this session only
+local screen             -- the builder of the screen on display
+local cur_cat            -- the category open in the code picker
+
+local function th(size) return ui.text_h and ui.text_h(size) or (size + 4) end
+local function btn_h() return th(14) + 14 end
+local function lines(text, width, size)
+  return ui.text_lines and ui.text_lines(text, width, size) or 1
+end
+
+local function go(fn)
+  screen = fn
+  clear()
+  fn()
+end
+
+-- ---- encode / decode -------------------------------------------------------
+
+local function has_code(c)
+  for i, v in ipairs(st.codes) do if v == c then return i end end
+end
+
+local function position()
+  local f = sys.gps and sys.gps()
+  if not f then return nil end
+  return string.format("%.4f,%.4f", f.lat, f.lon)
+end
+
+-- MECP/<sev>/<codes> <n>pax P05 <lat>,<lon> <note>. P05 ("At GPS coordinates")
+-- always sits right before the coordinates, so a picked P05 is not repeated.
+local function encode()
+  local parts = {}
+  for _, c in ipairs(st.codes) do
+    if not (c == "P05" and st.gps) then parts[#parts + 1] = c end
+  end
+  if st.pax > 0 then parts[#parts + 1] = st.pax .. "pax" end
+  if st.gps then
+    local pos = position()
+    if pos then parts[#parts + 1] = "P05 " .. pos end
+  end
+  if st.note ~= "" then parts[#parts + 1] = st.note end
+  return "MECP/" .. st.sev .. "/" .. table.concat(parts, " ")
+end
+
+-- Words for a MECP line, or nil. Finds the message anywhere in the text, so a
+-- "name: MECP/..." channel line decodes too. Unknown codes stay as they are.
+local function decode(text)
+  local sev, rest = tostring(text or ""):match("MECP/(%d)/(.*)$")
+  if not sev then return nil end
+  sev = tonumber(sev)
+  local words, note, at_pos = {}, {}, false
+  for tok in rest:gmatch("%S+") do
+    if tok == "P05" then
+      at_pos = true
+    elseif CODES[tok] then
+      words[#words + 1] = CODES[tok]
+    elseif tok:match("^%u%d%d$") then
+      words[#words + 1] = tok
+    elseif tok:match("^%d+pax$") then
+      words[#words + 1] = tok:match("^(%d+)") .. " people"
+    elseif tok:match("^%-?%d+%.?%d*,%-?%d+%.?%d*$") then
+      words[#words + 1] = "at " .. tok
+      at_pos = false
+    elseif tok:match("^@%d%d%d%d$") then
+      words[#words + 1] = "at " .. tok:sub(2, 3) .. ":" .. tok:sub(4, 5)
+    else
+      note[#note + 1] = tok
+    end
+  end
+  if at_pos then words[#words + 1] = CODES.P05 end
+  local s = (SEV[sev] or ("Severity " .. sev)) .. ": " .. table.concat(words, ", ")
+  if #note > 0 then s = s .. ' "' .. table.concat(note, " ") .. '"' end
+  return s, sev
+end
+
+-- ---- screens ---------------------------------------------------------------
+
+local compose, pick_severity, pick_category, pick_codes, pick_channel, confirm_mayday, show_heard
+
+local function title(text)
+  ui.label(text, PAD, PAD, 14, C.text)
+  return PAD + th(14) + 6
+end
+
+local function list_screen(heading)
+  ui.scroll(false)
+  local top = title(heading)
+  return ui.list(PAD, top, W - 2 * PAD, H - top - PAD)
+end
+
+local function do_send()
+  if #st.codes == 0 then sys.toast("Pick at least one code", 1500) return end
+  if not st.chan then go(pick_channel) return end
+  local text = encode()
+  if #text > MAX_LEN then sys.toast("Too long: " .. #text .. " of " .. MAX_LEN, 2000) return end
+  local ok, err, wait = mesh.send(st.chan, text)
+  if ok then
+    sys.toast("Sent to " .. st.chan, 1500)
+  elseif err == "rate limited" then
+    sys.toast("Sent too often, wait " .. tostring(wait or "a few") .. " s", 2500)
+  else
+    sys.toast("Not sent: " .. tostring(err), 2500)
+  end
+end
+
+compose = function()
+  ui.scroll(true)
+  local bw, bh = W - 2 * PAD, btn_h()
+  local half = math.floor((bw - PAD) / 2)
+  local y = PAD
+
+  ui.button("Severity: " .. SEV[st.sev], PAD, y, bw, bh, function() go(pick_severity) end)
+  y = y + bh + 4
+  ui.button(#st.codes == 0 and "Pick codes" or ("Codes: " .. #st.codes), PAD, y, bw, bh,
+            function() go(pick_category) end)
+  y = y + bh + 4
+  if #st.codes > 0 then
+    local names = {}
+    for _, c in ipairs(st.codes) do names[#names + 1] = c .. " " .. (CODES[c] or "") end
+    local text = table.concat(names, "\n")
+    local l = ui.label(text, PAD, y, 12, C.sub)
+    l:width(bw)
+    y = y + lines(text, bw, 12) * th(12) + 4
+  end
+  ui.button("People: " .. (st.pax > 0 and st.pax or "-"), PAD, y, half, bh, function()
+    ui.input("How many people", st.pax > 0 and tostring(st.pax) or "", function(t)
+      if t then st.pax = math.max(0, math.min(999, math.floor(tonumber(t) or 0))) end
+      go(compose)
+    end)
+  end)
+  ui.button("Position: " .. (st.gps and "on" or "off"), PAD + half + PAD, y, half, bh, function()
+    st.gps = not st.gps
+    go(compose)
+  end)
+  y = y + bh + 4
+  ui.button(st.note == "" and "Add a note" or ("Note: " .. st.note), PAD, y, bw, bh, function()
+    ui.input("Note (plain words)", st.note, function(t)
+      if t then st.note = t:gsub("[\r\n]", " "):gsub("^%s+", ""):gsub("%s+$", "") end
+      go(compose)
+    end)
+  end)
+  y = y + bh + 4
+  ui.button("Channel: " .. (st.chan or "pick one"), PAD, y, bw, bh, function() go(pick_channel) end)
+  y = y + bh + 6
+
+  local text = encode()
+  local too_long = #text > MAX_LEN
+  local pv = ui.label(text, PAD, y, 14, too_long and C.bad or (st.sev == 0 and C.bad or C.accent))
+  pv:width(bw)
+  y = y + lines(text, bw, 14) * th(14) + 2
+  if st.gps and not position() then
+    ui.label("No GPS fix: sent without a position", PAD, y, 12, C.sub)
+    y = y + th(12) + 2
+  end
+  y = y + 4
+
+  ui.button(st.sev == 0 and "Send MAYDAY" or "Send", PAD, y, half, bh, function()
+    if st.sev == 0 then go(confirm_mayday) else do_send() end
+  end)
+  ui.button("Decode", PAD + half + PAD, y, half, bh, function()
+    ui.input("MECP text", "MECP/", function(t)
+      if t then
+        local words, sev = decode(t)
+        if words then
+          table.insert(heard, 1, { from = "Decoded", raw = t, words = words, sev = sev })
+          while #heard > KEEP_HEARD do table.remove(heard) end
+          go(show_heard)
+          return
+        end
+        sys.toast("Not a MECP message", 1500)
+      end
+      go(compose)
+    end)
+  end)
+  y = y + bh + 4
+  ui.button("Heard (" .. #heard .. ")", PAD, y, half, bh, function() go(show_heard) end)
+  ui.button("Start over", PAD + half + PAD, y, half, bh, function()
+    st.sev, st.codes, st.pax, st.note = 3, {}, 0, ""
+    go(compose)
+  end)
+end
+
+pick_severity = function()
+  local l = list_screen("Severity")
+  for s = 0, 3 do
+    local i = l:add(SEV[s] .. ", " .. SEV_SUB[s], function() st.sev = s; go(compose) end)
+    if s == 0 then l:color(i or (s + 1), C.bad) end
+  end
+  l:select(st.sev + 1)
+end
+
+pick_category = function()
+  local l = list_screen("Codes: pick a category")
+  l:add("Done", function() go(compose) end)
+  for _, cat in ipairs(CATS) do
+    local n = 0
+    for _, c in ipairs(st.codes) do if c:sub(1, 1) == cat.id then n = n + 1 end end
+    local i = l:add(cat.id .. "  " .. cat.name .. (n > 0 and ("  (" .. n .. ")") or ""), function()
+      cur_cat = cat
+      go(pick_codes)
+    end)
+    if n > 0 and i then l:color(i, C.accent) end
+  end
+end
+
+pick_codes = function()
+  local l = list_screen(cur_cat.name)
+  l:add("Back", function() go(pick_category) end)
+  for _, code in ipairs(CAT_CODES[cur_cat.id] or {}) do
+    local function text() return (has_code(code) and "[x] " or "[ ] ") .. code .. " " .. CODES[code] end
+    local i
+    i = l:add(text(), function()
+      local at = has_code(code)
+      if at then table.remove(st.codes, at) else st.codes[#st.codes + 1] = code end
+      if i then
+        l:set(i, text())
+        l:color(i, has_code(code) and C.accent or C.text)
+      end
+    end)
+    if i and has_code(code) then l:color(i, C.accent) end
+  end
+end
+
+pick_channel = function()
+  local chans = mesh.channels and mesh.channels() or {}
+  local l = list_screen("Post to channel")
+  if #chans == 0 then l:add("No channels on this device", function() go(compose) end) return end
+  for _, name in ipairs(chans) do
+    local i = l:add(name, function()
+      st.chan = name
+      store.set("chan", name)
+      go(compose)
+    end)
+    if name == st.chan and i then l:select(i) end
+  end
+end
+
+confirm_mayday = function()
+  ui.scroll(true)
+  local bw, bh = W - 2 * PAD, btn_h()
+  local y = title("Send a MAYDAY?")
+  local msg = "A MAYDAY asks everyone who hears it for immediate help. It goes to "
+           .. tostring(st.chan or "the channel you pick") .. " as:\n" .. encode()
+  local l = ui.label(msg, PAD, y, 12, C.text)
+  l:width(bw)
+  y = y + lines(msg, bw, 12) * th(12) + 8
+  ui.button("Send MAYDAY", PAD, y, bw, bh, function() do_send(); go(compose) end)
+  y = y + bh + 4
+  ui.button("Cancel", PAD, y, bw, bh, function() go(compose) end)
+end
+
+show_heard = function()
+  ui.scroll(true)
+  local bw, bh = W - 2 * PAD, btn_h()
+  local y = PAD
+  ui.button("Back", PAD, y, bw, bh, function() go(compose) end)
+  y = y + bh + 6
+  if #heard == 0 then
+    local t = "Nothing yet. MECP messages on your channels show up here, decoded, while this app is open."
+    local l = ui.label(t, PAD, y, 12, C.sub)
+    l:width(bw)
+    return
+  end
+  for _, h in ipairs(heard) do
+    local head = h.from .. ": " .. h.words
+    local l = ui.label(head, PAD, y, 12, h.sev == 0 and C.bad or C.text)
+    l:width(bw)
+    y = y + lines(head, bw, 12) * th(12)
+    local r = ui.label(h.raw, PAD, y, 12, C.sub)
+    r:width(bw)
+    y = y + lines(h.raw, bw, 12) * th(12) + 8
+  end
+end
+
+-- ---- lifecycle -------------------------------------------------------------
+
+function app.on_message(m)
+  local words, sev = decode(m.text)
+  if not words then return end
+  local from = tostring(m.sender or "?")
+  if m.channel then from = m.channel .. ", " .. from end
+  table.insert(heard, 1, { from = from, raw = tostring(m.text), words = words, sev = sev })
+  while #heard > KEEP_HEARD do table.remove(heard) end
+  if sev == 0 then sys.toast(from .. ": " .. words, 5000) end
+  -- MECP traffic is rare, so a rebuild is cheap: the list grows, or the Heard
+  -- count on the compose screen moves.
+  if screen == show_heard or screen == compose then go(screen) end
+end
+
+function app.on_open(w, h)
+  W, H = w, h
+  if not mesh.send then
+    local l = ui.label("MECP needs a board with the extended app SDK (it posts to channels).",
+                       PAD, PAD, 14, C.text)
+    l:width(W - 2 * PAD)
+    return
+  end
+  local saved = store.get("chan")
+  local chans = mesh.channels and mesh.channels() or {}
+  for _, name in ipairs(chans) do
+    if name == saved then st.chan = name end
+  end
+  if not st.chan then
+    for _, name in ipairs(chans) do
+      if not st.chan and name:lower():find("emergency", 1, true) then st.chan = name end
+    end
+  end
+  go(compose)
+end
+
+function app.on_close() end
+
+return app